Tapes and Rods in the Metric System With the conversion to the Metric where we seldom measure distances more which is not consistent with the material System, Surveyors and Engineers have than 20 to 30 metres. A long tape is used. to change their tools to metric tapes subject to more abrasion when using the METRIC RODS and rods. This change brings many un­ reel. This means, the markings in the The levelling rods have also specific certainties when it comes to choosing first 10 metres could be more easily points like the above-described tapes, the proper tapes and rods. damaged than on a shorter tape. The which should be considered. Any good effect of fish-tailing of the end of the METRIC TAPES metric rod should have even and odd- tape causes metal fatigue and leads to numbered metres shown in a different Ontario Ministries, Municipalities breaking of the tape in the first metre, colour. For instance; red on white or and private companies have experiment­ or so. A light and smooth end-piece is black on white, orange on white or any ed with various devices and graduations preferable to a heavy, easy-catching type. other distinct combination. in the last few months, or even years, to find an answer to their individual require­ Recommended lengths for tapes are As with the tapes, the five unit ments and needs as far as the metric 50m, 30m, or even 25m. For layout of concept should be adhered to. The best tape is concerned. engineering stations at 25m intervals, in this line is the rod marked with E’s it might be advisable to use a 25m tape where each bar of the “E” is one centi­ The main feature of any tool in the instead of 30m tape, for easier location metre in width. Any smaller graduation Metric System is the clear and unmis­ of the individual stations. Occasionally, is confusing and does not add to the takable graduation into 5 units. On a a 100m tape might be required. This accuracy in the reading to the nearest tape, it should be a distinct mark every type of tape should be graduated in mm. Any instrument-man can estimate 5th centimetre, or millimetre. This grad­ centimetres only and each graduation to the nearest millimetre after a very uation, in five equally wide spaces, is should be high, or deep-etched into the short time of practice. Each decimetre preferred because the human eye can steel for longer wear. on the rod should be clearly marked, as easily visualize the five graduations in to the metre and decimetre, which is in one glance. Any different graduation, The Northern Drag Tape, or Babbit the visual field of the instrument. Do other than 5 units, will confuse the eye Tape is a useless tool in any system, not buy any rod which causes you to and give cause for errors in reading the Imperial or Metric. The soldered metal count the spaces between two marked tape. It, also, slows down the work con­ pieces at each interval are inaccurate points. It increases the occurance of siderably. and each section of tape has a different errors and the time required to take a weight. Such tapes are unsuitable for reading. The changeover from the Imperial any accurate surveying work since they The markings on the rod should be System to the S.I. System should be do not lead to proper sag corrections. well protected against wear-and-tear in made totally, and no tape should have The modern fibreglass tapes are the trunk of the car, or on the truck. dual markings. Such tapes give rise to This can be accomplished by having a unnecessary mistakes, especially when well manufactured and can be applied to certain types of jobs. Jobs involved folding rod with the marked faces all the instrument man is reading the tape on the inside of the folded rod. The on a long distance and the tape is twisted, with Engineering surveys, surveys of small house lay-outs, surveys which are refacing of any rod, marked in Imperial or the wind turns the tape to the wrong measurements with plastic metric gradu- markings. relevant to hydro power lines, or pipe­ lines which created static electricity (see uated facing, is not recommended. There Alaska Pipeline explosions) and survey is no guaranty that the facing will be Add-tapes, as they were used in properly glued on. Each individual rod the Imperial System, are not common measurements across main traffic arteries which all call for the use of non-metallic may have an error in its graduation. and not desirable in the Metric System. This error can fluctuate when there are The tape in the Imperial System was tapes. But, we must also give careful consideration to the accuracy which can several sections individually glued on. graduated in feet, and only the first and This can cause gross errors if the rod last foot was graduated into hundredths be expected from this type of tape. A good fibreglass tape is specified to be is read in different sections, or different of a foot. Therefore, an addition of one rods are used alternately on the job. foot on the zero-end of the tape, in accurate to within 2mm for a length of reverse numbers, made it easy to read ten metres, or 0.02%, if the pull is in One specific type of rod should be the proper distance. This type of arrange­ accordance with the manufacturer’s spec­ mentioned here; the one-piece rod in 4 ment in the Metric System is neither ification. Any non-metallic tape should to 5 metre lengths for precise levelling feasible nor practical, since each metric be graduated in centimetres. Any gradu­ to first order accuracy. The rod should tape should be fully graduated into spaces ation smaller than the above mentioned also be graduated in centimetres. The not exceeding one centimetre. If the party is giving rise to an illusion of accuracy, one-piece rod is essential for this type of chief is not sure that his rear chainman which no reputable manufacturer will accuracy, since it has no constant or can estimate or read the tape properly, provide, in order “not” to put his repu­ inconsistent accumulating errors as have let the rear chainman hold the zero-end, tation at stake. The recommended gradu­ the commonly used sliding rods. The and the head chainman can read the ation will enable any intelligent chain­ sliding rods have a great drawback, as it chain in the centimetre graduation to man to estimate the distance to the near­ is entirely up to the rodman how long the nearest millimetre without much est millimetre, after a relatively short time the rod is extended. This could result trouble. No tape should be pulled more of practice. Requirements for millimetre in considerable errors, when you want than the tension suggested by the manu­ graduation on non-metallic tapes are to run a level loop to a relatively high facturer. sometimes requested in specifications, but standard of accuracy (2nd or 3rd order). are very hard to manufacture and give In the Metric System, the folding rod is The length of the tapes or chains cause to more inaccuracy than the above more widely used than any other rod. should be considered in the light of cer­ suggested estimation by the surveyor’s H. J. Koester, O.L.S., Chairman tain requirements for efficient use. A assistant. In other words, do not expect Metric Task Force 50-metre tape is not feasible for work higher accuracy by smaller graduations Association of Ontario Land Surveyors THE ONTARIO LAND SURVEYOR, SUMMER 1978 29.