AUG 13 1971 -^4 UNITED STATES DEPARTMENT OF COMMERCE 161670 C. R. SMITH, Secretary
NATIONAL BUREAU OF STANDARDS / a. v. astin, Director
Special Publication 304A. Issued 1968.
lUj h Brief History and Use of THE ENGLISH AND METRIC SYSTEMS OF MEASUREMENT with a CHART OF THE MODERNIZED METRIC SYSTEM
"Weights and measures may be ranked among the necessaries of life to every individual of human society. They enter into the eco- nomical arrangements and daily concerns of every family. They are necessary to every occupation of human industry; to the distribution and security of every species of property; to every transaction of
trade and commerce ; to the labors of the husbandman ; to the in-
genuity of the artificer; to the studies of the philosopher ; to the researches of the antiquarian, to the navigation of the mariner, and the marches of the soldier; to all the exchanges of peace, and all the operations of war." —JOHN QUINCY ADAMS
When the American Colonies sepa- sembly of France on May 8, 1790, of the length of a great circle of the rated from the mother country to to enact a decree, sanctioned by Louis earth. This idea found favor with the assume among the nations of the XVI, which called upon the French French philosophers at the time of the earth a separate and individual sta- Academy of Sciences in concert with French Revolution, men who were tion, they retained, among other the Royal Society of London to "de- generally opposed to any vestige of things, the weights and measures duce an invariable standard for all of monarchical authority and preferred that had been used when they were the measures and all weights." Hav- a standard based on a constant of colonies, namely, the weights and ing already an adequate system of nature. measures of England. It is probable weights and measures, the English The French Academy assigned the that these were at that time the most were not interested in the French name metre (meter), from the Greek firmly established and widely used undertaking, so the French proceeded metron, a measure, to the unit of weights and measures in the world. with their endeavor alone. The result length which was supposed to be one England a highly coherent nation, is what is known as the metric system. ten millionth of the distance from separated by sea from many of the The metric system was conceived the north pole to the equator, along turmoils of the European continent, as a measurement system to the base the meridian running near Dunkirk, had long before established stand- ten: that is, the units of the system, Paris, and Barcelona. An attempt was ards for weights and measures that their multiples, and submultiples made to measure this meridian from have remained essentially unchanged should be related to each other by northern France to southern France, up to the present time. The yard, simple factors of ten. This is a great from which the true distance from established by Henry II, differs only convenience because it conforms to the pole to the equator could be by about 1 part in a thousand from our common system for numerical no- calculated. The best techniques then the yard of today. The pound of tation, which is also a base ten system. available were used. Although the op- Queen Elizabeth I shows similar Thus to convert between units, their erations were carried out during a
agreement with the present avoir- multiples, and submultiples. it is not politically disturbed time, the results dupois pound. necessary to perform a difficult mul- were in error only by about 2000 No such uniformity of weights and tiplication or division process, but meters, a remarkable achievement in measures existed on the European simply to shift the decimal point. those days. continent. Weights and measures dif- The system seems to have been first Meanwhile the National Assembly fered not only from country to coun- proposed by Gabriel Mouton, a vicar had preempted the geodetic survey, try, but even from town to town and of Lyons, France, in the late 17th cen- upon which the meter was to be based, from one trade to another. This lack tury. He proposed to define the unit and established a provisional meter. of uniformity led the National As- of length for the system as a fraction The unit of mass called the gram was
For sale by the Superintendent of Documents, U.S. Government Printing Office, Washington, D.C. 20402 — Price 20 cents 1 0;
The Modernized Metric Syt
M E 1 8 i 7 9 1 0 Centimeter-! j 1 2 | 4 LLuJ,j,,ii,l!d,.,i,,I ! ii,,Li,..,L,,LL,L.iJ 11, iiiiiiLiiiii
' 1 ' W ' ill ' m Inchu 1>3 lU ' 1*6 ' VS VI 1'8 119 1 INCH 1 FOOT Y A
1,1,1,1,1,1,1, 1, J, I 1, 1, 1, nl,l,l,l,ln, I, ill, 1, 1,1,1,1,1, 1,1, 1,1, lJ.1.1, 1, 1,1,1,1, 1,1,1, 1, 1,1,1, 1,1,1,1,1^^ 1.1, 1,1, 1, 1,1,1, 1,1,1, 1,1,1,1,1,1,1,1, ill, 1,1,1, hi,!,!, I 1, 1,1.1,1,1,1,1, 1, 1,1, 1,1, 1,1,1,1,1
THE International System of Units— viated SI —is a modernized version
1 :ub c c ECI METER 1 LIQUID QUART system. It was established by inter also called (approximately) I liter 0.946 liter ment to provide a logical and interconnec
] 00c cm for all measurements in science, industry,
SI is built upon a foundation of base units
nitions, which appear on this chart. All oil The Six Base Units of Measured!
The meter is defined as 1 650 763.73 wavelengths in The second is defined as the duration of 9 192 631 The standard for the unit of mass, the kilogram, is a vacuum of the orange-red line of the spectrum of 770 cycles of the radiation associated with a specified cylinder of platinum-iridium alloy kept by the Inter- krypton-86. transition of the cesium atom. It is realized by tun- national Bureau of Weights and Measures at Paris. ing an oscillator to the resonance frequency of the A duplicate in the custody of the National Bureau of cesium atoms as they pass through a system of mag- Standards serves as the mass standard for the United nets and a resonant cavity into a detector. States. This is the only base unit still defined by an artifact.
DIRECTION OF MAGNETIC FIELD
U.S. PROTOTYPE
An interferometer is used to measure length by means of light waves.
Closely allied to the concept of mass is that of FROM OSCILLATOR force. The SI unit of force is the newton (N). A force of 1 newton, when applied for 1 second, will give to of atomic beam spectrometer. The trajectories A schematic an a 1 kilogram mass a speed of 1 meter per second are drawn for those atoms whose magnetic moments are The SI unit of area is the square meter (m ). Land (an acceleration of 1 meter per second per second). "flipped" in the transition region. is often measured by the hectare (10 000 square meters, or approximately 2.5 acres).
The SI unit of volume is the cubic meter (m ). Fluid volume is often measured by the liter (0.001 cubic The number of periods or cycles per second is meter). called frequency. The SI unit for frequency is the —- ACCELERATION OF lm/j' 1968 hertz (Hz). One hertz equals one cycle per second. Standard frequencies and correct time are broad- Is 2 cast from NBS stations WWV, WWVB, WWVH, and One newton equals approximately two tenths of a WVWL, and stations of the U.S. Navy. pound of force. Many shortwave receivers pick up WWV on fre- The weight of an object is the force exerted on it quencies of 2.5, 5, 10, 15, 20, and 25 megahertz. by gravity. Gravity gives i mass l downward accelera- National Bureau of Standards Special Publication 304 A The standard radio broadcast band extends from tion of about 9.8m s (Supersedes Miscellaneous Publication 232) 535 to 1605 kilohertz. The SI unit for work and energy of any kind is For sale by the Superintendent of Documents, U.S. Government Dividing distance by time gives speed. The SI unit the joule (J). Printing Office, Washington, D.C. 20402 - Price 20 cents for speed is the meter per second (m/s), approxi- 1J — 1 N • lm mately 3 feet per second. References: The SI unit for power of any kird is the watt (W). Rate of change in speed is called acceleration. NBS Handbook 102, ASTM Metric Practice Guide, 40 cents The SI unit for acceleration is the meter per second NBS Misc. Publ. 247, Weights and Measures Standards of the iw= 4^ United States, A Brief History, 35 cents per second (m/s=). Is NBS Misc. Publ. 286. Units of Weight and Measure, Definitions and Tables of Equivalents, $1.50
Special Publication This chart is one-third the actual size of the full-scale wall chart, NBS 304, which is availabl m A '
U.S. DEPARTMENT OF COMMERCE ^mrmr^ The International System of Units (SI) National Bureau of Standards ' 6,0 S „i„j ,, m l„i,,,l,i,Ii,!!i,,Jm„i ,,,,i j LL,LJi.a.i.iJ L±, lj lj l.l i ,.i SLlu i ,LuLa,, - l| l |l l| l |l l| ll|l|l l | | | | W^^ | « 1 1 1 1 1 1 1 1 1 1 1 1 3l4 1 3l5 1 zl« 2I3 214 m« 2l5 zk 2l7 2>S 219 3l0 3ll 3l2 3l3 D 2 FEET '''''''''''' llhlllllllllLlliJllllllllllllllllllllllllllllllll^ ially abbre- derived from these base units. Multiples and submultiples The kilogram shown here approximates one third the metric are expressed in a decimal system. Use of metric weights the size of the platinum-iridium standard of mass. One pound of the same material would be three tional agree- and measures was legalized in the United States in 1866, times the size shown below. i framework and our customary units of weights and measures are de- 1 pound = 0.453 592 37 kg S commerce, fined in terms of the meter and the kilogram. The only d their defi- legal units for electricity and illumination in the United Sl units are States are SI units. definitions, abbreviations, ent and some SI units derived from them ;the thermodynamic or Kelvin scale of temperature The ampere is defined as the magnitude of the cur- The candela is defined as the luminous intensity of jused in SI has its origin or zero point at absolute zero rent that, when flowing through each of two long 1 600 000 of a square meter of a radiating cavity land has a fixed point at the triple point of water de- parallel wires separated by one meter in free space, at the temperature of freezing platinum (2042 K). ifined as 273.16 kelvins. The Celsius scale is derived results in a force between the two wires (due to their LIGHT EMITTED HERE jrrom the Kelvin scale. The triple point is defined as magnetic fields) of 2x10 ' newton for each meter of 0.01 °C on the Celsius scale, which is approximately length. 1A 32.02 °F on the Fahrenheit scale. The relationship of The SI unit of light flux is I source the Kelvin, Celsius, and Fahrenheit temperature t t I the lumen (lm). A lm FORCE = 2 x 10-' N scales is shown below. having an intensity of 1 in all THERMOMETER WATER - i 111 candela directions BOILS it {(ELECTRICAL - 1A radiates a light flux of 4 RESISTANCE TYPE) [«—lm-»| lumens. INSULATING The SI unit of voltage is the volt (V). MATERIAL 1W BODY _ 310.15 37 IV = TEMPERATURE 1A The SI unit of electrical resistance is the ohm (;>). A 100-watt light bulb emits about 1700 lumens IV 1 WATER VAPOR l a - WATER ...273.15 JJ.0 --32 1A FREEZES COMMON EQUIVALENTS AND CONVERSIONS 233.15 4J--40 THESE PREFIXES MAY BE APPLIED .+ Approximate Common Equivalents Conversions Accurate to Parts Per Million 1 inch -.25 millimeters inches x 25,4" —millimeters TO ALL SI UNITS 1 foot -0.3 meter feet x 0.3048' -meters °? 1 yard -0.9 meter yards x 0.9144* -meters and Submultiples ABSOLUTE Mo 1L -273.15 J 1 mile =1,6 kilometers miles x 1.609 34 ^kilometers Multiples ZER07\ 1 square inch =6.5 sq centimeters square inches x 6.4516* —sq centimeters 1 square foot 0.D9 square meter square feet x 0.092 903 0 .-square meters 1 OOO 000 OOO OOO 10" tera (ter'a) T REENTRANT o o 1 square yard O.B square meter square yards x 0.836 127 .^square meters 1 OOO 10 giga (jl'ga) G . OOO OOO WELL KELVIN CELSIUS FAHRENHEIT 1 acre 0.4 hectare f acres x 0.404 6B6 —hectares 1 cubic inch 16 cu centimeters cubic inches x 16.3871 = cu centimeters « 1 OOO OOO 10« mega (meg' a) M REFRIGERATING 1 cubic foot 0.03 cubic meter cubic feet x 0.028 31G 8 — cubic meters 1 cubic cubic yards x 0.764 555 —cubic meters • BATH cubic yard 0.8 meter lOOO 10' kilo (kil o) k 1 quart (tq) ---1 liter quarts (|q)x 0.946 353 =liters f — 1 gallon 0.004 cubic meter gallons x 0 003 7B5 41 cubic meters 100 10= hecto (nek 'to) h Temp F+40=1.8(Temp C+40) t ounce (avdp} - 28 grams ounces (avdp) x 23.349 5 ^grants 1 pound (avdp) 0.45 kilogram pounds (avdp) i 0.453 592 -kilograms 10 10 deka (dek'a) da F=1.8(Temp Temp C)+32 1 horsepower =0.75 kilowatt horsepower i 0.745 700 — kilowatts O.l 10 ' deci (des'i) d Temp C=(Temp F-32)/1.8 - 1 millimeter 0.04 inch millimeters x 0.039 370 1 = inches • Temp K=Temp C+273.15 1 meter -. 3.3 teet meters x 3.280 84 —feet 0.01 io-= centi (sen ' ti) c 1 meter . 1.1 yards meters x 1.093 61 =: yards TRIPLE POINT CELL 3 • 1 kilometer 0.6 mile kilometers x 0.621 371 -miles O.OOl 10- milli (mil'i) m 1 sq centimeter 0.16 square inch sq centimeters x 0.155 DM --square inches triple 6 • The point cell, an evacuated glass cylinder 1 square meter = 11 square teet square meters i 10.7639 — square feet 0.000 001 10- micro (mi'kro) 1 square meter 12 square yards square meters x 1.195 ^square yards filled with pure water, is used to define a known fixed 99 0.000 OOO OOl 10-» nano (nan'o) n 1 hectare + -2.5 acres hectares x 2.471 05 temperature. When the until 1 cell is cooled a mantle cu centimeter 0 06 cubic inch cu centimeters x 0.061 023 7 -cubic inches = 0.000 OOO OOO OOl 10' pico (pe ' ko) P 1 -35 cubic feet x teet of ice forms around the reentrant well, the tempera- cubic meter cubic meters 35.3147 =cubie 1 — cubic meter .1.3 cubic yards cubic meters t 1.307 95 cubic yards 0.000 OOO OOO OOO OOl 10" femto (fern 'to) f ture at the interface of solid, liquid, and vapor is 1 liter t =1 quart (lq) liters x 1.056 69 —quarts (lq) t cubic meter . 250 gallons cubic meters x 264.172 ^gallons 10-" a 0.01 °C. Thermometers to be calibrated are placed 0.000 OOO OOO OOO OOO OOl atto (at to) 1 gram 0.035 ounces (avdp] grams » 0.035 274 0 = ounces (avdp) in the reentrant well. 1 kilogram 2.2 pounds (avdp) kilograms x 2.204 62 ^pounds (avdp) 1 kilowatt =1.3 horsepower kilowatts x 1.341 02 -horsepower n term not used in SI •Most commonly used om the Superintendent of Documents, U.S. Government Printing Office, Washington, D.C. 20402, for 50 cents. 1 J — *»«-«-.%•«-»* m U S DEPARTMENT ( The Modernized Metric System and its relationship to U.S. customary units METER - — : International System of Units— officially abbre- derived from these base units. Multiples and submultiples THE are viated SI—is a modernized version of the metric expressed in a decimal system. Use of metric weights system. It was established by international agree- and measures was legalized in the United States in 1866. ment to provide a logical and interconnected framework and our customary units of weights and measures are de- for all measurements in science, industry, and commerce. fined in terms of the meter and the kilogram. The only legal SI is built upon a foundation of base units and their defi- units for electricity and illumination in the United as nitions, which appear on this chart. All other SI units are States are SI units. The Six Base Units of Measurement t 1 t 1 — l|iS :::2=_ COMMON EQUIVALENTS AND CONVERSIONS 0.000 OM 001 10-' wTwiTb n 10-" ' 0.000 000 000 000 000 001 Iili'JiVrt) i. ing Office, Washington, I Britain soon had vast investments in of Weights and Measures. Also es- a highly industrialized society based tablished was the General Conference on their own system. of Weights and Measures, which The new metric system found much would meet every six years to con- favor with scientists of the 19th cen- sider any needed improvements in tury, partly because it was intended the standards and to serve as the to be an international system of authority governing the International measurement, partly because the units Bureau. An International Committee of measurement were theoretically of Weights and Measures was also supposed to be independently re- set up to implement the recommenda- as the mass of one cubic decided on producible, and partly because of the tions of the General Conference and centimeter of water at its temperature simplicity of its decimal nature. to direct the activities of the Interna- of density. Since this was maximum These scientists proceeded to derive tional Bureau: this Committee meets too small a quantity to be measured new units for the various physical every two years. with the desired precision the deter- quantities with which they had to Since its inception nearly 175 years on one cubic mination was made deal, basing the new units on ele- ago, the number of countries using decimeter of water, but even at that mentary laws of physics and relating the metric system has been growing the results found to be in error were them to the units of mass and length rapidly. The original metric system by about 28 parts in a million. Thus, of the metric system. The system of course had imperfections: and it the meter that was established as the found increasing acceptance in vari- has since undergone many revisions, foundation of the system did not ap- ous European countries which had the more recent ones being accom- proximate the idealized definition on been plagued by a plethora of unre- plished through the General Confer- which it was based with the desired lated units for different quantities. ence of Weights and Measures. An accuracy. Also the unit of mass dif- Because of increasing technological extensive revision and simplification fered from the idealized definition development there was a need for in 1960 by the then 40 members of even as given in terms of the errone- international standardization and im- the General Conference resulted in a ously defined meter. So the new sys- provements in the accuracy of stand- modernized metric system—the Inter- metal- tem was actually based on two ards for units of length and mass. national System of Units—which is lic standards not differing greatly in This led to an international meeting described in detail in the accompany- nature from the yard of Henry II or in France in 1872, attended by 26 ing chart. the pound of Elizabeth I. countries including the United States. As a unit for fluid capacity, the The meeting resulted in an interna- founders selected the cubic decimeter tional treaty, the Metric Convention, NOTE: For further information see and as a unit for land area they se- which was signed by 17 countries, the references listed on the chart. lected the are, equal to a square ten including the United States in 1875. In addition, a more complete treat- meters on the side. In this manner, This treaty set up well defined metric ment of the English and metric sys- while decimal relationships were pre- standards for length and mass, and tems of measurement will soon be served between the units of length, established the International Bureau available. fluid capacity, and area, the relation- ships were not kept to the simplest possible form. Although there was ^CONVENTION OF THE METER| some discussion at the time of deci- malizing the calendar and the time of day. the system did not include any DIPLOMATIC unit for time. The British system of weights and measures, and the metric system as well, had been developed primarily TECHNICAL for use in trade and commerce rather than for purposes of science and en- gineering. ELECTRICITY Because technological achievement PHOTOMETRY TEMPERATURE depends to a considerable extent upon LENGTH the ability to make phvsical measure- TIME ments, the Americans and the Brit- IONIZING RADIATIONS ish proceeded to adapt their system of UNITS measurements to the requirements of the new technology of the 19th cen- GCWM: GENERAL CONFERENCE OF WEIGHTS AND MEASURES tury, despite the fad that the newly ICWM: INTERNATIONAL COMMITTEE OF WEIGHTS AND MEASURES developed metric system seemed to BIPM: INTERNATIONAL BUREAU OF WEIGHTS AND MEASURES have certain points of superiority. INTERNATIONAL COORDINATION OF MEASUREMENT STANDARDS Both the United States and Great U. S. GOVERNMENT PRINTING OFFICE : 1069 O - 325-509 — UNITED STATES DEPARTMENT OF COMMERCE FREDERICK B. DENT, Secretary NATIONAL BUREAU OF STANDARDS / RICHARD W. ROBERTS, Director Special Publication 304 A. Reissued September, 1974 Brief History of MEASUREMENT SYSTEMS with a Chart of the Modernized Metric System "Weights and measures may be ranked among the necessaries of life to every individual of human society. They enter into the eco- nomical arrangements and daily concerns of every family. They are necessary to every occupation of human industry; to the distribu- tion and security of every species of property; to every transaction of trade and commerce; to the labors of the husbandman; to the in- genuity of the artificer; to the studies of the philosopher; to the researches of the antiquarian, to the navigation of the mariner, and the marches of the soldier; to all the exchanges of peace, and all the operations of war. The knowledge of them, as in established use, is among the first elements of education, and is often learned by those who learn nothing else, not even to read and write. This knowledge is riveted in the memory by the habitual application of it to the em- ployments of men throughout life." JOHN QUINCY ADAMS Report to the Congress, 1821 Weights and measures were among and measure more complex things—it The "yard" as a measure of length the earliest tools invented by man. was also necessary to do it accurately can be traced back to the early Saxon Primitive societies needed rudimentary time after time and in different places. kings. They wore a sash or girdle measures for many tasks: constructing However, with limited international ex- around the waist—that could be re- dwellings of an appropriate size and change of goods and communication of moved and used as a convenient measur- shape, fashioning clothing, or bartering ideas, it is not surprising that different ing device. Thus the word "yard" comes food or raw materials. systems for the same purpose developed from the Saxon word "gird" meaning Man understandably turned first to and became established in different parts the circumference of a person's waist. parts of his body and his natural sur- of the world—even in different parts of Standardization of the various units roundings for measuring instruments. a single continent. and their combinations into a loosely Early Babylonian and Egyptian records related system of weights and measures and the Bible indicate that length was sometimes occurred in fascinating ways. The English System first measured with the forearm, hand, Tradition holds that King Henry I de- or finger and that time was measured by The measurement system commonly creed that the yard should be the dis- the periods of the sun, moon, and other used in the United States today is nearly tance from the tip of his nose to the heavenly bodies. When it was necessary the same as that brought by the colo- end of his thumb. The length of a fur- to compare the capacities of containers nists from England. These measures had long (or furrow-long) was established such as gourds or clay or metal vessels, their origins in a variety of cultures by early Tudor rulers as 220 yards. This they were filled with plant seeds which Babylonian, Egyptian, Roman, Anglo- led Queen Elizabeth I to declare, in the were then counted to measure the vol- Saxon, and Norman French. The an- 16th century, that henceforth the tradi- umes. When means for weighing were cient "digit," "palm," "span," and tional Roman mile of 5,000 feet would invented, seeds and stones served as "cubit" units evolved into the "inch," be replaced by one of 5,280 feet, mak- standards. For instance, the "carat," still "foot," and "yard" through a compli- ing the mile exactly 8 furlongs and pro- used as a unit for gems, was derived cated transformation not yet fully un- viding a convenient relationship between from the carob seed. derstood. two previously ill-related measures. As societies evolved, weights and Roman contributions include the use Thus, through royal edicts, England measures became more complex. The of the number 12 as a base (our foot is by the 18th century had achieved a invention of numbering systems and the divided into 12 inches) and words from greater degree of standardization than science of mathematics made it possible which we derive many of our present the continental countries. The English to create whole systems of weights and weights and measures names. For exam- units were well suited to commerce and measures suited to trade and commerce, ple, the 12 divisions of the Roman trade because they had been developed land division, taxation, or scientific re- "pes," or foot, were called unciae. Our and refined to meet commercial needs. search. For these more sophisticated words "inch" and "ounce" are both de- Through colonization and dominance of uses it was necessary not only to weigh rived from that Latin word. world commerce during the 17th, 18th, For sale by the Superintendent of Documents. U.S. Government Printing Office, Washington. D.C. 20402 Stock No. 0303-01073 THE MODERNIZED Illlrlr^ metric LENGTH MASS The second is dt cycles of the ra transition of the system tuning an oscin cesium-133 aton The International System of Units-SI r agnets and a i is a modernized version of the metric system established by international ScfWRWtlc dtaQfwn of rrujojntfJc moments * agreement. It provides a logical and interconnected framework for all 1 IK S3! 770 Mdlla measurements in science, industry, and commerce. Officially abbreviated SI, the system is built upon a foundation of seven base units, plus two supplementary units, which appear on this chart along with their defini- tions. All other SI units are derived from these units. Multiples and sub- multiples are expressed in a decimal system. Use of metric weights and measures was legalized in the United States in 1866, and since 1893 the ELECTRIC CURRENT yard and pound have been defined in terms of the meter and the kilogram. The base units for time, electric current, amount of substance, and lumi- nous intensity are the same in both the customary and metric systems. COMMON CONVERSIONS MULTIPLES AND PREFIXES The kelvin isdet Accurate to Six Significant Figun These Prefixes May Be Applied To AM SI Unils tion 1/273.16 of namic temperati Symbol When You Know Multiply by To Find Symb Multiples and Submultiples Prefixes Symbols point of water. T B OK is called "ab in inches *25.4 millimeters mm 10' ' I 000 000 000 000 lera(tera) T TEMPERATURE ft feet *0.3048 melers m 1000 000 000 IV giqn{|iga) G yd yards ' 0.91 44 meters m 1 000 000 lO*- mcqn (meg'a) M mi miles 1.609 34 kilometers km 3 yd-' square yards 0.836 127 square meters m ? 1 000 10 kilo (kilo") k acres 0.404 686 checlares ha yd3 cubic yards 0.764 555 cubic meters m 3 10 10' deka (dek a) da qt quarts (Iq) 0.946 353 °liters I Base Unit 1 10" oz ounces (avdp) 28.349 5 grams g lb pounds (avdp) 0 453 592 kilograms kg 0.1 10' dccrfdes'O d °F Fahrenheit *5 9(aflersub Celsius °C 0.01 10 * centi (scn'li) c OUNTOF SUBSTANt temperature trading 32) temperature VJAJ 3 0 001 10 milh (mil i) m 0 000 001 10 ° micro (rrii'kro) \i 0 039 370 1 inches in 0 000 000 001 10 9 nano (nan o) n 3.280 84 feel ft 1.093 61 yards yd 0000 000 000 001 10" pico(pe'ko) p kilometers 0 621 371 miles mi •* 0 000 000 000 000 001 10. lemlo.(lem'to) . f ? [rftiiT' square meters 1 195 99 square yards yd ih 1B allo(al'to) c 0 000 000 000 000 000 001 10 a teM hectares 2.471 05 acres 3 cubic meters 1 307 95 cubic yards yd LUMINOUS INTENSITY "liters 1.056 69 quarts (Iq) qt National Bureau of Standards grams 0 035 274 0 ounces (avdp) oz Special Publication 304A i Revised October 1972) kilograms 2.204 62 pounds (avdp) lb For sale by trie Suponntcndcnl of Documents. U.S. Government Printing Office, Washinqton, D C. 20402 *9/5 Celsius (then Fahrenheit °F SDCal.ilogNo.CI3 10: 304A - Price 75 cents temperature add 32) temperature REFERENCES NQS Spcct.il Publication 330. 1972 Edition. International System of Unils (SI), available by purchase from the Superintendent of Documenls. Government Printing Office. Washington. D.C. 20402. order as 013.10 330/2; 30 cents a copy. "lor example, l in 25 4 mm. so 3 inches would be m ASTM Metric Practice Quid" E380-72. available by pur- in) |25 4 ™ chase from the Amuriran Society for Testing and (3 ) 762 mm The radian Is the Materials. 1916 Race Street. Philadelphia. Pa. 19103. c h iBc-B vertex at the cer nectar* is a common name for 10 000 square meters SI .50 a minimum 7m copy, order S3.00. D [ subtended by an liter is a common name for fluid volume of 0 001 cubic meter SI Units and Recommendations for the Use ol Their Multiples and of Certain Oilier Units, order as ISO Stand- the radius. Note; Most symbols are written with lower case letters, exceptions are ard 1000. $1.50 a copy, from the American National PLANE ANGLE unils named after persons for which the symbols are capitalized. Standards Institute. 1430 Broadway. N.Y.. N.Y. 10018. Periods are nol used with any symbols. INCHE 1 YAPtrv 1 .1.1.1.2 34 56 7891 ) 11 12 13 14 15 16 17 , 1 I l i l l i l l i l i l l l i 1 l l |l T r T - - - ' l l Tri i n i i ni r-(' r'i'i iH- r-h i -Wi iW' i !|V'W 'i (V'l'i 0^''VhM'i 'W'Vl i' 10 20 CENTIMETERS Mini A full-scale wall chart, NBS Special Publication 304 (Revised October 1972,) is available from the f u 2 U.S. DEPARTMENT OF COMMERCE SEVEN BASE UNITS National Bureau of Standards 1 650 76173 WAVELENGTHS - The SI unit of area is the square meter (m '). national spelling, metre) wavelengths in vacuum ol / ML WAVELENGTH The SI unit of volume is the cubic meter (m>). The spectrum of krypton-86. liter (0.001 cubic meter), although not an SI unit, is A A\AAAAAA/ commonly used to measure fluid volume. J \# W An Interferon*interferometer le used to measure length by means of light waves The SI unit for pressure is the pascal (Pa). in = i for the unit of mass, the kilogram, is a The SI unit of force is the newton (N). 1Pa 1N/m* ilatinum-iridium alloy kept by the Interna- One newton is the force which, when The SI unit for work and energy of any u s. prototype 1 j of Weights and Measures at Paris. A du- applied to a kilogram mass, will give kind i the (J). - :celeration s joule of of s custody the National Bureau Stand- rY the kilogram mass an acceleration of -oMm/s" 1J = 1N-m is the mass standard for the United States, 1 (meter per second) per second. The SI unit for power of any kind is the nly base unit still defined by an artifact. 1N = 1kg-m/s2 watt (W). 1W = 1J/s OSCILLATING FIELD the duration of 9 192631 770 TRANSITION REGION (CAVITY) The number of periods or cycles per second CESIUM issociated with a specified SOURCE is called frequency. The SI unit for frequency , Standard frequencies correct -133 atom. It is realized by is the hertz (Hz). One hertz equals one cycle and time are ie resonance frequency of per second. broadcast from WWV, WWVB. and WWVH, and stations of the U.S. Navy. Many short- y pass through a system of DEFLECTION MAGNET The SI unit for speed is the meter per second cavity into a detector. wave receivers pick up WWV and WWVH, on (m/s). frequencies of 2 5, 5, 10, 15, and 20 megahertz. team spectrometer or "dock." Onry those atoms whose The SI unit for acceleration is the (meter per ' In the transition region reach ths detector When ! occurred, the clock Indicates one second has passed second) per second (m/s ). The SI unit of voltage is the volt (V). pere is defined as that current which, if maintained in each of two 1V = 1W/A rallel wires separated by one meter in free space, would produce FORCE =2x10"'N between the two wires (due to their magnetic fields) of 2 x 10"7 The SI unit of electric resistance is the ohm (O). for each meter of length. 1*fi = 1V/A 1 •*>![' TEMPERATURE The standard temperature at the triple VAPOR Water MEASUREMENT On the commonly used Celsius temperature scale, wa- THERMOMETER WATER " (ELECTRICAL point of water is provided by a special i SYSTEMS ter freezes at about 0 and boils at about 100 °C. The °C RESISTANCE cell, an evacuated glass cylinder contain- °C is defined as an interval of 1 K, and the Celsius tem- TYPE) Body Temperature ing pure water. When the cell is cooled perature 0 is defined as 273.15 K. °C until a mantle of ice forms around the re- 0 Water Freezes- entrant well, the temperature at the inter- 1.8 Fahrenheit degrees are equal to 1.0 °C or 1.0 K; face of solid, liquid, and vapor is 273.16 K. the Fahrenheit scale uses 32 °F as a temperature cor- Thermometers to be calibrated are placed responding to 0 °C. FAHRENHEIT °F in the reentrant well. When the mole is- used, the elementary The mole is the amount of substance of entities must be specified and may be The SI unit of concentration (of amount of a system that contains as many elemen- atoms, molecules, ions, electrons, other substance) is the mole per cubic meter tary entities as there are atoms in 0.01 3 particles, or specified groups of such (mol/m ). kilogram of carbon 12. particles. The candela is defined as the luminous The SI unit of light flux is the lumen intensity of 1/600 000 of a square meter (Im). A source having an intensity of 1 of a blackbody at the temperature of candela in all directions radiates a light freezing platinum (2045 K). flux of 4 7T lumens. TWO SUPPLEMENTARY UNITS ,ea W U Bl] iy L* 1 The steradian is the solid angle with ^rr^-v. ~~atL? J A 1 J ri, 1 1 its vertex at the angle with Its M raoianV\\ Bb/i —1 Td r| '— -a i center of a sphere /mlrJ^^W circle that is 1 r that is subtended by an area of the / f ^1 ai l J K L L, al in length to I ^^^-< spherical surface equal to that of a wL [ . \ SOLID ANGLE ess?"******** j^^aa^ ident of Documents, U.S. Government Printing Office, Washington, D.C. 20402 V > KlMftlilnllEi SOLID ANGLE YARD — and 19th centuries, the English system pacity (volume) and mass (weight) system coincided with an age of of weights and measures was spread to were to be derived from the unit of rapid technological development. In the and established in many parts of the length, thus relating the basic units of United States, by Act of Congress in world, including the American colonies. the system to each other and to nature. 1866, it was made "lawful throughout However, standards still differed to an Furthermore, the larger and smaller the United States of America to employ extent undesirable for commerce among versions of each unit were to be created the weights and measures of the metric the 13 colonies. The need for greater by multiplying or dividing the basic system in all contracts, dealings or court uniformity led to clauses in the Articles units by 10 and its multiples. This fea- proceedings." of Confederation (ratified by the origi- ture provided a great convenience to By the late 1860's, even better metric nal colonies in 1781) and the Constitu- users of the system, by eliminating the standards were needed to keep pace tion of the United States (ratified in need for such calculations as dividing with scientific advances. In 1875, an in- 1790) giving power to the Congress to by 16 (to convert ounces to pounds) or ternational treaty, the "Treaty of the fix uniform standards for weights and by 12 (to convert inches to feet). Simi- Meter," set up well-defined metric stand- measures. Today, standards supplied to lar calculations in the metric system ards for length and mass, and estab- shifting all the States by the National Bureau of could be performed simply by lished permanent machinery to recom- Standards assure uniformity throughout the decimal point. Thus the metric sys- mend and adopt further refinements in the country. tem is a "base-10" or "decimal" system. the metric system. This treaty, known The Commission assigned the name as the Metric Convention, was signed by metre (which we also spell meter) to 17 countries, including the United The Metric System the unit of length. This name was de- States. The need for a single worldwide coor- rived from the Greek word metron, As a result of the Treaty, metric dinated measurement system was recog- meaning "a measure." The physical standards were constructed and distrib- nized over 300 years ago. Gabriel Mou- standard representing the meter was to uted to each nation that ratified the ton, Vicar of St. Paul in Lyons, proposed be constructed so that it would equal Convention. Since 1893, the interna- in 1670 a comprehensive decimal meas- one ten-millionth of the distance from tionally agreed-to metric standards have urement system based on the length of the north pole to the equator along the served as the fundamental weights and one minute of arc of a great circle of meridian of the earth running near Dun- measures standards of the United States. the earth. In 1671 Jean Picard, a French kirk in France and Barcelona in Spain. By 1900 a total of 35 nations—in- astronomer, proposed the length of a The metric unit of mass, called the cluding the major nations of continental - pendulum beating seconds as the unit "gram,' was defined as the mass of one Europe and most of South America of length. (Such a pendulum would cubic centimeter (a cube that is 1/100 had officially accepted the metric sys- have been fairly easily reproducible, of a meter on each side) of water at its tem. Today, with the exception of the thus facilitating the widespread distribu- temperature of maximum density. The United States and a few small countries, tion of uniform standards.) Other pro- cubic decimeter (a cube 1/10 of a meter the entire world is using predominantly posals were made, but over a century on each side) was chosen as the unit of the metric system or is committed to elapsed before any action was taken. fluid capacity. This measure was given such use. In 1971 the Secretary of Com- In 1790, in the midst of the French the name "liter." merce, in transmitting to Congress the Revolution, the National Assembly of Although the metric system was not results of a 3-year study authorized by France requested the French Academy accepted with enthusiasm at first, adop- the Metric Study Act of 1968, recom- of Sciences to "deduce an invariable tion by other nations occurred steadily mended that the U.S. change to pre- standard for all the measures and all the after France made its use compulsory dominant use of the metric system weights." The Commission appointed by in 1 840. The standardized character and through a coordinated national pro- the Academy created a system that was, decimal features of the metric system gram. The Congress is now considering at once, simple and scientific. The unit made it well suited to scientific and en- this recommendation. of length was to be a portion of the gineering work. Consequently, it is not The International Bureau of Weights earth's circumference. Measures for ca- surprising that the rapid spread of the and Measures located at Sevres, France, serves as a permanent secretariat for the Metric Convention, coordinating the ex- change of information about the use and refinement of the metric system. As measurement science develops more pre- cise and easily reproducible ways of de- fining the measurement units, the Gen- eral Conference of Weights and Meas- ures—the diplomatic organization made up of adherents to the Convention meets periodically to ratify improve- ments in the system and the standards. In 1960, the General Conference adopted an extensive revision and sim- plification of the system. The name Le Systeme International a" Unites (Inter- national System of Units), with the in- ternational abbreviation SI, was adopted for this modernized metric system. Fur- ther improvements in and additions to SI were made by the General Confer- ence in 1964, 1968, and 1971. - eights and "span," and "cubit" units measures were evolved into the "inch," among the earliest "foot," and "yard" through a tools invented by complicated transformation not man. Primitive yet fully understood. societies needed Roman contributions include rudimentary the use of the number 12 as a measures for many tasks: constructing base (our foot is divided into dwellings of an appropriate size and 12 inches) and words from shape, fashioning clothing, or bartering which we derive many of our food or raw materials. present weights and measures Man understandably turned first to names. For example, the 12 parts of his body and his natural divisions of the Roman "pes," surroundings for measuring instruments. or foot, were called unciae. Early Babylonian and Egyptian records Our words "inch" and and the Bible indicate that length was "ounce" are both derived from WITH A CHART OF THE first measured with the forearm, hand, that Latin word. or finger and that time was measured by The "yard" as a measure of MODERNIZED the periods of the sun, moon, and other length can be traced back to the METRIC SYSTEM heavenly bodies. When it was necessary early Saxon kings. They wore a to compare the capacities of containers sash or girdle around the fa fa Weights and measures may be such as gourds or clay or metal vessels, waist that could be removed ranked among the necessaries of life to they were filled with plant seeds which and used as a convenient every individual of human society. They were then counted to measure the measuring device. Thus the enter into the economical arrangements volumes. When means for weighing word "yard" comes from the and daily concerns of every family. They were invented, seeds and stones served Saxon word "gird" meaning are necessary to every occupation of as standards. For instance, the "carat," the circumference of a person's human industry; to the distribution and still used as a unit for gems, was waist. security of every species of property; to derived from the carob seed. Standardization of the every transaction of trade and As societies evolved, weights and various units and their commerce; to the labors of the measures became more complex. The combinations into a loosely husbandman; to the ingenuity of the invention of numbering systems and the related system of weights and artificer; to the studies of the science of mathematics made it possible measures sometimes occurred philosopher; to the researches of the to create whole systems of weights and in fascinating ways. Tradition antiquarian, to the navigation of the mariner, and the marches of the soldier; measures suited to trade and commerce, holds that King Henry I land division, taxation, or scientific decreed that the yard should be to all the exchanges of peace, and all the operations of war. The knowledge of research. For these more sophisticated the distance from the tip of his them, as in established use, is among uses it was necessary not only to weigh nose to the end of his thumb. the first elements of education, and is and measure more complex things—it The length of a furlong (or often learned by those who learn was also necessary to do it accurately furrow-long) was established by nothing else, not even to read and write. time after time and in different places. early Tudor rulers as 220 This knowledge is riveted in the memory However, with limited international yards. This led Queen by the habitual application of it to the exchange of goods and communication Elizabeth I to declare, in the employments of men throughout life.^fa of ideas, it is not surprising that 16th century, that henceforth different systems for the same purpose the traditional Roman mile of JOHN QUINCY ADAMS the 1821 developed and became established in 5 000 feet would be replaced Report to Congress, different parts of the world—even in by one of 5 280 feet, making ' ' ' ' ' ' ' I I I I I I I I different parts of a single continent. the mile exactly 8 furlongs and providing a convenient relationship between two previously of weights and measures was spread to ill- related measures. and established in many parts of the THE ENGLISH SYSTEM Thus, through royal edicts, England world, including the American colonies. by the 18th century had achieved a However, standards still differed to The measurement system commonly greater degree of standardization than an extent undesirable for commerce used in the United States today is nearly the continental countries. The English among the 13 colonies. The need for the same as that brought by the units were well suited to commerce and greater uniformity led to clauses in the colonists from England. These measures trade because they had been developed Articles of Confederation (ratified by had their origins in a variety of and refined to meet commercial needs. the original colonies in 1781) and the cultures—Babylonian, Egyptian, Through colonization and dominance of Constitution of the United States Roman, Anglo-Saxon, and Norman world commerce during the 17th, 18th, (ratified in 1790) giving power to the French. The ancient "digit," "palm," and 19th centuries, the English system Congress to fix uniform standards for « oHI oIS) QC £C UJ < 5 O "SiU °o ~ c Z 9 p s s< 3 CO co co CO O "O re c « E .-s -c g « u 2 E "See q.w O u ~ -n re (0 2.2 3 .2 »£tjs "o S > „ O 0) c )I « *- CO « W Q.~ w c E "E "S <" "re - i: e . „, .h .9- Z E c B = $o O a>~ E S — " ; c « 4 3 « <§3° 8 _ O -i:§l8re cu .«^OcS f 2 0) E cn I « re o S XI £ CD Q- c re 3 re E o O E § CD 3 ~ o => 05 ST « E -a &v re cd ci> CD CD > O. jc .52 E E Ill o 111 CD r; CO « 5 W o 51C — tO (0 (ft % a> C Q) CO o E ™ iu 1! £ (5 CO , UDC (/>- H u "111 X -5 o 2 X . CO z § s § -IU £ CD T3 c .0 " C D E _ fS E c5 2 to 3 CO * 111 53 o- CO CD -c co E 1 E E J E c o o a si c b: S B fc g S 2 j5 " • = Ejll?5! S • 55l?l5 «> CT O O F o ^ o g CD Pi OJ o —ssi-Oi-orsotDf^ V U) UJ T V ttJ S W S N O 3 O ID i- T CD ~Z Ecypp'-OOOO O ^ W E o 2 © c E E I E g o f ?sB > E » £ E « E 8 e l. S 0 n ^ o J E ii E o o £ 5 * o o S = = — m m O = O -D ™ W 0> 3 • 5e cr o Ct Cc tC ^ m o o- o M 1 l INCHES i i i° i 7 .T. i.T.i. T. i.T.i. T. ,.T.,.T.,.f.,. T.,. 1 1 1 1 1 1 1 1 1 1 1 1 f 1 1 1 I'l'i'i'i Ml ' '1 1 1MM 1 M'l 1 1 '1 1 'I' 1 1 1 1 1 i f [' 1' W 'P 1 P 1 'T' 1 f'T 1 H 'T I f P x 1 CENTIMETERS *> so 1 so — weights and measures. Today, standards The physical standard representing the recommend and adopt further supplied to all the States by the meter was to be constructed so that it refinements in the metric system. This National Bureau of Standards assure would equal one ten-millionth of the treaty, known as the Metric uniformity throughout the country. distance from the north pole to the Convention, was signed by 17 equator along the meridian of the earth countries, including the United States. THE METRIC running near Dunkirk in France and As a result of the Treaty, metric SYSTEM Barcelona in Spain. standards were constructed and The metric unit of mass, called the distributed to each nation that ratified The need for a single worldwide "gram," was defined as the mass of one the Convention. Since 1893, the coordinated measurement system was cubic centimeter (a cube that is 1/100 internationally agreed-to metric recognized over 300 years ago. Gabriel of a meter on each side) of water at its standards have served as the Mouton, Vicar of St. Paul in Lyons, temperature of maximum density. fundamental weights and measures proposed in 1670 a comprehensive standards of the United States. decimal measurement system based on By 1900 a total of 35 nations the length of one minute of arc of a including the major nations of great circle of the earth. In 1671, Jean continental Europe and most of South Picard, a French astronomer, proposed America—had officially accepted the the length of a pendulum beating metric system. In 1971 the Secretary of seconds as the unit of length. (Such a Commerce, in transmitting to Congress pendulum would have been fairly easily the results of a 3-year study authorized reproducible, thus facilitating the by the Metric Study Act of 1968, widespread distribution of uniform recommended that the U.S. change to standards.) Other proposals were made, predominant use of the metric system but over a century elapsed before any through a coordinated national action was taken. program. The Congress responded by In 1790 in the midst of the French enacting the Metric Conversion Act of Revolution, the National Assembly of 1975. Today, with the exception of a France requested the French Academy few small countries, the entire world is of Sciences to "deduce an invariable The cubic decimeter (a cube 1/10 of a using the metric system or is changing standard for all the measures and all meter on each side) was chosen as the to such use. the weights." The Commission unit of fluid capacity. This measure The International Bureau of Weights appointed by the Academy created a was given the name "liter." and Measures located at Sevres, system that was, at once, simple and Although the metric system was not France, serves as a permanent scientific. The unit of length was to be accepted with enthusiasm at first, secretariat for the Meter Convention, a portion of the earth's circumference. adoption by other nations occurred coordinating the exchange of Measures for capacity (volume) and steadily after France made its use information about the use and mass (weight) were to be derived from compulsory in 1840. The standardized refinement of the metric system. As the unit of length, thus relating the character and decimal features of the measurement science develops more basic units of the system to each other metric system made it well suited to precise and easily reproducible ways of and to nature. Furthermore, the larger scientific and engineering work. defining the measurement units, the and smaller versions of each unit were Consequently, it is not surprising that General Conference on Weights and to be created by multiplying or the rapid spread of the system Measures—the diplomatic organization dividing the basic units by 10 and its coincided with an age of rapid made up of adherents to the powers. This feature provided a great technological development. In the Convention—meets periodically to convenience to users of the system, by United States, by Act of Congress in ratify improvements in the system and eliminating the need for such 1866, it was made "lawful throughout the standards. calculations as dividing by 16 (to the United States of America to employ In 1960, the General Conference convert ounces to pounds) or by 12 the weights and measures of the metric adopted an extensive revision and (to convert inches to feet). Similar system in all contracts, dealings or simplification of the system. The name calculations in the metric system could court proceedings." Le Systeme International d'Unites be performed simply by shifting the By the late 1860's, even better metric (International System of Units), with decimal point. Thus the metric system standards were needed to keep pace the international abbreviation SI, was is a "base- 10" or "decimal" system. with scientific advances. In 1875, an adopted for this modernized metric The Commission assigned the name international treaty, the "Treaty of the system. Further improvements in and metre—meter—to the unit of length. Meter," set up well-defined metric additions to SI were made by the This name was derived from the Greek standards for length and mass, and General Conference in 1964, 1968, word metron, meaning "a measure." established permanent machinery to 1971, 1975, 1979, and 1983. , 2 COPY "Weights and measures may be eighfsflnd A ranked among the necessaries of life to A Brief ; '& measles _ every individual of human society. They were! jfl enter into the economical arrangements among the and daily concerns of every family. They HISTORY earliest are necessary to every occupation of tools invented by man. Primitive human industry; to the distribution and of Measurement societies needed rudimentary security of every species of property; to for tasks: every transaction of trade and Systems measures many commerce; to the labors of the constructing dwellings of an husbandman; to the ingenuity of the WITH A CHART OF THE appropriate size and shape, artificer; to the studies of the MODERN METRIC SYSTEM fashioning clothing, and bartering philosopher; to the researches of the food or raw materials. antiquarian, to the navigation of the mariner, and the marches of the soldier; Man understandably turned to all the exchanges of peace, and all first parts of his body and his to the operations of war. The knowledge of natural surroundings for measuring them, as in established use, is among instruments. Early Babylonian and the first elements of education, and is Egyptian records, and the Bible, often learned by those who learn indicate that length was first nothing else, not even to read and write. measured with the forearm, hand, or This knowledge is riveted in the memory by the habitual application of it to the finger and that time was measured employments of men throughout life." by the periods of the sun, moon, and other heavenly bodies. When it was JOHN QUINCYADAMS necessary to compare the capacities Report to the Congress, 1821 of containers such as gourds or clay or metal vessels, they were filled with plant seeds that were then counted to measure the volumes. With the development of scales as a systems for the same purpose the words from which we derive be the distance from the tip of his means for weighing, seeds and developed and became established many of our present measurement nose to the end of his outstretched stones served as standards. For in different parts of the world unit names. For example, the 1 thumb. The length of a furlong (or instance, the "carat," still used as a - even in different parts of the divisions of the Roman "pes," or furrow-long) was established by mass unit for gems, is derived from same country. foot were called unciae. Our words early Tudor rulers as 220 yards. This the carob seed. "inch" and "ounce" are both derived led Queen Elizabeth I to declare, in THE ENGLISH SYSTEM from that Latin word. the 1 6th century, that henceforth As societies evolved, the traditional Roman mile of 5000 measurements became more The measurement system The "yard" as a measure of feet would be replaced by one of complex. The invention of commonly used in the United States length can be traced back to early 5280 feet making the mile exactly numbering systems and the science today is nearly the same as that Saxon kings. They wore a sash or eight furlongs and providing a of mathematics made it possible to brought by the colonists from girdle around the waist that could be convenient relationship between the create whole systems of England. These measures had their removed and used as a convenient furlong and the mile. measurement units suited to trade origins in a variety of cultures - measuring device. The word "yard" and commerce, land division, Babylonian, Egyptian, Roman, comes from the Saxon word "gird" Thus, through royal edicts, taxation, and scientific research. For Anglo-Saxon, and Norman French. meaning the circumference of a England by the 1 8th century had these more sophisticated uses, it was The ancient "digit," "palm," "span," person's waist achieved a greater degree of necessary not only to weigh and and "cubit" units of length slowly lost standardization than other European measure more complex things - it preference to the length units "inch," Standardizing various units and countries. The English units were was also necessary to do it "foot," and "yard." combining them into loosely related well suited to commerce and trade accurately time after time and in systems of measurement units because they had been developed different places. However, with Roman contributions include sometimes occurred in fascinating and refined to meet commercial limited international exchange of the use of 1 2 as a base number (the ways. Tradition holds that King needs. Through English colonization goods and communication of ideas, it foot is divided into 1 2 inches) and Henry I decreed that a yard should and its dominance of world is not surprising that different 1 ?~- W) +J 01 3 7 12 £ u o 15 o 3 U 1 1 1 e 1 1 « N 1 1 Iff iiijiH 1. 0> f = 5 5o Q. V : 2 2 2 2 2 2 1 I I § I I § § 2 5 = 8888888 " 6 e E S § § § I I 1 I § § § § § §~ d £§§§§§ " i § i § I 1 1 i I 1 § °1§§ "*> <- - « " 5 I 111" I E II i n ir 1 r "** •' •i ? a - z « * »i "V «1! "V 111 .5 o = E E'ut E E E EEEEE-^E^^E -EE 1 « i ii* I S I 5 *: I I IJ II 5- ^ Ifl I SI 1 H» 1 E £j" ir S * "g. f- | 1 E Te-' -5 l"-g \S-Si iriiiiiiiiiiiii.tiiiitfiii til fi, v..- o 111 l^r b iiiiiiidAriihii ju ill I! * ii in The meter is the length of the path traveled The standard for the unit of mass, the by light in vacuum during a time interval of kilogram, is a cylinder of platinum-iridium alloy 1/299 792 158 of a second. kept by the International Bureau ofWeights 1 METER and Measures near Paris.A duplic I I custody of the National Institute;e JL. „ 1/299 792 458 OF A SECOND of Standards and Technology serve as the mass standard 4 for the United States. SI unit of speed is the The meter per This is the only base second (m/s). the modern metric system unit still defined by The International System of Units (SI), the modem version of the metric an artifact. The speed of light in vacuum is 299 792 4. system, is established by international agreement. It provides a logical and meters per second. The SI unit of interconnected framework for all measurements in science, industry, and force is the commerce. Officially abbreviated SI, the system is built upon a foundation (N). SI unit of acceleration is the newton The meter of seven base units, shown on this chart along with their descriptions. All per second per second 1 One newton (m/s ). other SI units are derived from these units. Multiples and submultiples are is a force that, expressed using a decimal system. Use of metric units was legalized in the applied to a one The SI unit of area is the square meter United States in 1866. Since 1893 the yard and pound have been defined in kilogram object, (m'). SI unit of volume is the cubic The terms of the meter and the kilogram.The base units for time, electric 1 will give the objea meter (m ). The liter cubic decimeter) (1 current, amount of substance, and luminous intensity are the same in both an acceleration of although not an SI unit, is accepted for use the inch-pound and metric systems. with the SI and is commonly used to one meter per second > fluid votur per second. 1 1 N - U -mis The weight of an object is the force exerted on it by gravity. Gravity gives a mass a downward 1 acceleration of about 9.8 m/s . The SI unit for pressure is the pascal (Pa), 2 1 Pa = 1 N/m The ampere is that current which, if The kelvin is the fraction 1 /273.1 6 of the maintained in each of two infinitely long thermodynamic temperature of the triple The SI unit for work and energy of any kind parallel wires separated by one meter in fret point of water. The temperature 0 K is is the joule (J). space, would produce a force between the commonly referred to as "absolute zero." = 1 J 1 N-m two wires (due to their magnetic fields) of On the widely used Celsius temperature 0" The second is the duration of 7 2 x 1 newtons for each meter of length. The SI unit for power of any kind is the 9 1 92 63 1 770 cycles of the radiation freezes at 0 °C watt (W). associated with a specific transition of the = r and boils at 1 W 1 J/s cesium 1 33 atom. The second is realized by T about 1 00 °C. tuning an oscillator to the resonance One Celsius frequency associated with the above degree is an definition. Just before entering a microwave interval of 1 K, cavity, cesium atoms are forced into the right and zero atomic state by a laser beam. A detector degrees Celsius is 273.15 K. An interval of reglsters a signal only when the oscillator one Celsius degree corresponds to an delivers just the right frequency to the The SI unit of electric interval of 1.8 Fahrenheit degrees on the microwave cavity causing transitions and potential difference Fahrenheit temperature scale. changing the state of the atoms. This change is the volt (V). = in state is sensed at the detector. 1 V 1 W/A The standard temperature at the triple point of water is provided by a special cell, an The mole is the The SI unit of amount of substance of a evacuated glass cylinder containing pure system electric resistance that contains as many elementary water. When the cell is cooled enough so entities as there are is the ohm (12). atoms in 0.012 kilogram that a mande of G of carbon 1 2, 1 fi = 1 V/A , ice forms around Thi imber of periods or cycles per second the reentrant When the mole is used, the elementary is called frequency. The SI unit for frequency well, the tem- entities must be specified and may be atoms, Is the hertz (Hz). One hertz Is the same as molecules, perature at the ions, electrons, other particles, or one cycle per second. Standard frequencies specified interface of solid, groups of such particles. and the cornea time are broadcast by radio liquid, and vapor stations WWV andWWVB in Colorado, and The SI unit of concentration (of amount of s 273.1 6 K. Thermometers to be calibrated WWVH in Hawaii. N 1ST delivers digital substance) is the mole per cubic meter ire placed in the n 3 timing signals by telephone and through the (mol/m ). The candela is the luminous intensity, in a given direction, of a source that emits monochromatic radiation of frequency 11 540 x 10 hertz (Hz) and that has a radiant intensity in that direction of 1/683 v steradian. Radiation at frequencies other than 13 540 x 10 Hz is also measured in candelas in accordance with the standard luminous efficiency, V( A), curve that peaks at 1 540 x 10' Hz (yellow-green). 3 6 7 commerce during the 1 7th, 1 8th, The Commission appointed by the occurred steadily after France made system. Seven units - the meter and 1 9th centuries, the English Academy created a system that was, its use compulsory in 1 840. The (for length), the kilogram (for mass), system of measurement units at once, simple and scientific. The standardized structure and decimal the second (for time), the ampere became established in many parts unit of length was to be a portion of features of the metric system made (for electric current), the kelvin (for of the world, including the the Earth's circumference. Measures it well suited for scientific and thermodynamic temperature), the American colonies. for capacity (volume) and mass were engineering work. Consequently, it mole (for amount of substance), to be derived from the unit of is not surprising that the rapid and the candela (for luminous However, standards still length, thus relating the basic units of spread of the system coincided with intensity) ~ were established as the differed to an extent undesirable for the system to each other and to an age of rapid technological base units for the system. The name commerce, even among the 1 nature. Furthermore, larger and development In the United States, Systeme International d'Unites American colonies. The need for smaller multiples of each unit were by Act of Congress in 1 866, it (International System of Units), greater uniformity led to clauses in to be created by multiplying or became "lawful throughout the with the international abbreviation the Articles of Confederation dividing the basic units by 1 0 and its United States of America to employ SI, was adopted for this modern (ratified by the original colonies in powers. This feature provided a the weights and measures of the metric system. 1 781 ) and the Constitution of the great convenience to users of the metric system in all contracts, United States (ratified in 1 790) that system, by eliminating the need for dealings or court proceedings." In 1971, the U.S. Secretary of gave Congress the power to fix such calculations as dividing by 1 Commerce, in transmitting to uniform standards for weights and (to convert ounces to pounds) or by By the late 1 860s, even better Congress the results of a 3-year measures. Today, standards supplied 1 2 (to convert inches to feet). metric standards were needed to study authorized by the Metric to all the states by the National Similar calculations in the metric keep pace with scientific advances. Study Art of 1 968, recommended Institute of Standards and system could be performed simply In 1 875, an international agreement that the U.S. change to predominant Technology assure uniformity by shifting the decimal point Thus, known as the Meter Convention, set use of the metric system through a throughout the country. the metric system is a "base-10" or up well-defined metric standards for coordinated 1 0-year national "decimal" system. length and mass and established program. The Congress responded THE METRIC SYSTEM permanent mechanisms to by enacting the Metric Conversion The Commission assigned the recommend and adopt further Act of 1 975, calling for voluntary The need for a single name metre - meter -- to the unit refinements in the metric system. conversion. Amendments to the Act worldwide coordinated of length. This name was derived This agreement commonly called in 1 988 designated the metric measurement system was from the Greek word metron, the 'Treaty of the Meter" in the system as the "preferred system of recognized over 300 years ago. meaning "a measure." The physical United States, was signed by 1 weights and measures for United Gabriel Mouton.Vicar of Si Paul's standard representing the meter was countries, including the United States trade and commerce." Church in Lyons and an astronomer, to be constructed so that it would States. As a result of the Treaty, proposed in 1 670 a comprehensive equal one ten-millionth of the metric standards were constructed Measurement science decimal measurement system based distance from the North Pole to the and distributed to each nation that continues to develop more precise on the length of one minute of arc equator along the meridian running ratified the Convention. Since 1 893, and easily reproducible ways of of a great circle of the Earth. near Dunkirk in France and the internationally adopted-to defining measurement units. The Mouton also proposed the swing Barcelona in Spain. metric standards have served as the working organizations of the length of a pendulum with a fundamental measurement standards General Conference on Weights and frequency of one beat per second as The initial metric unit of mass, of the United States. Measures coordinate the exchange the unit of length. A pendulum with the "gram," was defined as the mass of information about the use and this beat would have been fairly of one cubic centimeter (a cube that By 1 900 a total of 35 nations refinement of the metric system and easily reproducible, thus facilitating is 0.01 meter on each side) of water -- including the major nations of make recommendations concerning the widespread distribution of at its temperature of maximum continental Europe and most of improvements in the system and its uniform standards. Other proposals density. The cubic decimeter South America -- had officially related standards. The General were made, but more than a century (a cube 0.1 meter on each side) accepted the metric system. Conference meets periodically to elapsed before any action was taken. was chosen as the unit for capacity. ratify improvements. Additions and The fluid volume measurement for In 1 960, the General improvements to SI were made by In 1 790, in the midst of the the cubic decimeter was given the Conference on Weights and the General Conference in 1 964, French Revolution, the National name "liter." Measures, the diplomatic 1967-1968,1971,1975,1979, Assembly of France requested the organization made up of the 1983, 1991, and 1995. French Academy of Sciences to Although the metric system signatory nations to the Meter "deduce an invariable standard for all was not accepted with enthusiasm Convention, adopted an extensive the measures and all the weights." at first adoption by other nations revision and simplification of the Nisr U.S. DEPARTMENT OF COMMERCE Technology Administration National Institute of Standards and Technology