SAN FRANCISCO JULY 22-26 Volume 19, Number 3, 1985 Issues and Techniques in Touch-Sensitive Tablet Input William Buxton Ralph Hill Peter Rowley Computer Systems Research Institute University of Toronto Toronto, Ontario Canada M5S 1A4 (416) 978-6320 1. Introduction Increasingly, research in human-computer interac- Abstract tion is focusing on problems of input [Foley, Wallace Touch-sensitive tablets and their use in human- &Chan 1984; Buxton 1983; Buxton £985]. Much of computer interaction are discussed, It is shown this attention is directed towards input technolo- that such devices have some important properties gies. The ubiquitous Sholes keyboard is being that differentiate them from other input devices replaced and/or complemented by alternative tech- (such as mice and joysticks). The analysis serves nologies. For example, a major focus of the market- two purposes: (1) it sheds light on touch tablets, ing strategy for two recent personal computers, the and (2) it demonstrates how other devices might be Apple Macintosh and Hewlett-Packard 150, has been approached. Three specific distinctions between on the input devices that they employ (the mouse touch tablets and one button mice are drawn. These and touch-screen, respectively). concern the signaling of events, multiple point sensing and the use of templates. These distinc- Now that the range of available devices is expand- tions are reinforced, and possible uses of touch ing, how does one select the best technology for a tablets are illustrated, in an example application. particular application? And once a technology is chosen, hove can it be used most effectively? These Potential enhancements to touch tablets and other questions are important, for as Buxton [ 1983] has input devices are discussed, as are some inherent argued, the ways in which the user physiccdty problems. The paper concludes with recommenda- interacts with an input device have a marked effect tions for future work. on the type of user interface that can be effectiveIy supported. CR Categories and Subject Descriptors: 1.3.1 [Com- puter Graphics]: Hardware Architecture: Input Dev- In the general sense, the objective of this paper is ices. 1.3.6 [Computer Graphics]: Methodology and to help in the selection process and assist in Techniques: Device Independence, Ergonomics, effective use of a specific class o:F devices. Our Interaction Techniques. approach is to investigate a specific class of dev- ices: touch-sensitive tablets. We will identify touch General Terms: Design, Human Factors. tablets, enumerate their important properties, and Additional Keywords and Phrases: touch sensitive compare them to a more common input device, the input devices. mouse. We then go on to give examples of transac- tions where touch tablets can be used effectively. Permission to copy without fee all or part of this material is granted There are two intended benefits for this approach. provided that the copies are not made or distributed for direct First, the reader will acquire an understanding of commercial advantage, the ACM copyright notice and the title of the touch tablet issues. Second, the reader will have a publication and its date appear, and notice is given that copying is by concrete example of how the technology can be permission of the Association for Computing Machinery. To copy investigated, and can utilize the approach as a otherwise, or to republish, requires a fee and/or specific permission. model for investigating other classes of devices. 2. Touch-Sensitive Tablets A touch-sensitive tablet (touch tablet for short) is a flat surface, usually mounted horizontally or nearly horizontally, that can sense the location of a finger pressing on it. That is, it is a tablet that can sense © 1985 ACM 0-89791-166-0/85/007/0215 $00.75 that it is being touched, and where it is being 215 @ S I G G R A P H '85 touched. Touch tablets can vary greatly in size, most two mice at a time: one in each hand. Given from a few inches on a side to several feet on a side. that we have ten fingers, it is conceivable that we The most critical requirement is that the user is may wish to indicate more than two points simul- not required point with some manually held device taneously. An example of such an application such as a stylus or puck. appears below). What we have described in the previous paragraph • Unlike joysticks and trackballs, they have a very is a simple touch tablet. 0nly one point of contact low profile and can be integrated into other is sensed, and then only in a binary, touch/no touch, equipment such as desks and low-profile key- mode. One way to extend the potential of a simple boards (e.g., the Key Tronic Touch Pad, see touch tablet is to sense the degree, or pressure, of Appendix A). This has potential benefits in port- contact. Another is to sense multiple points of con- able systems, and, according to the Keystroke tact. In this case, the location (and possibly pres- model of Card, Newell and Moran [19S0], reduces sure) of several points of contact would be homing time from the keyboard to the pointing reported. Most tablets currently on the market are device. of the "simple" variety. However, Lee, Buxton and Smith [ 1985], and Nakatani [private communica- • They can be molded into one-piece constructions tion] have developed prototypes of multi-touch, thus eliminating cracks and grooves where dirt multi-pressure sensing tablets. can collect. This makes them well suited for very clean environments (eg. hospitals) or very dirty We wish to stress that we will restrict our discus- ones (eg., factories). sion of touch technologies to touch tablets, which • Their simple construction, with no moving parts, can and should be used in ways that are different leads to reliable and long-lived operation, making from touch screens. Readers interested in touch- them suitable for environments where they will screen technology are referred to Herot & Weinsap- be subjected to intense use or where reliability fel [1978], Nakatani & Rohrlich [1983] and Minsky is critical. [1984]. We acknowledge that a fiat touch screen mounted horizontally is a touch tablet as defined They do, of course, have some inherent disadvan- above. This is not a contradiction, as a touch screen tages, which will be discussed at the close of the has exactly the properties of touch tablets we paper. describe below, as long as there is no attempt to In the next section we will make three important mount a display below (or behind) it or to make it distinctions between touch tablets and mice. These the center of the user's visual focus. are: Some sources of touch tablets are listed in Appen- • Mice and touch tablets vary in the number and dix A. types of events that they can transmit. The difference is especially pronounced when com- 3. Properties of Touch-Sensitive Tablets paring to simple touch tablets. Asking "Which input device is best?" is much like • Touch tablets can be made that can sense multi- asking "How long should a piece of string be?" The ple points of contact. There is no analogous pro- answer to both is: it depends on what you want to perty for mice. use it for. With input devices, however, we are lim- ited in our understanding of the relationship • The surface of a tablet can be partitioned into between device properties and the demands of a regions representing a collection of independent specific application. We will investigate touch "virtual" devices. This is analogous to the parti- tablets from the perspective of improving our tioning of a screen into "windows" or virtual understanding of this relationship. Our claim is displays. Mice, and other devices that transmit that other technologies warrant similar, or even "'relative change" information, do not lend them- more detailed, investigation. selves to this mode of interaction without con- suming display real estate for visual feedback. Touch tablets have a number of properties that dis- With conventional tablets and touch tablets, tinguish them from other devices: graphical, physical or virtual templates can be • They have no mechanical intermediate device placed over the input device to delimit regions. (such as stylus or puck). Hence they are useful This allows valuable screen real estate to be in hostile environments (e.g., classrooms, public preserved. Physical templates, when combined access terminals) where such intermediate dev- with touch sensing, permit the operator to sense ices can get lost, stolen, or damaged. the regions without diverting the eyes from the primary display during visually demanding tasks. • Having no puck to slide or get bumped, the track- ing symbol "stays put" once placed, thus making After these properties are discussed, a simple them well suited for pointing tasks in environ- finger painting program is used to illustrate them ments subject to vibration or motion (e.g., fac- in the context of a concrete example. We wish to tories, cockpits). stress that we do not pretend that the program represents a viable paint program or an optimal . They present no mechanical or kinesthetic res- interface. It is simply a vehicle to illustrate a trictions on our ability to indicate more than one variety of transactions in an easily understandable point at a time. That is, we can use two hands or context. more than one finger simultaneously on a single tablet. (Remember, we can manually control at 216 SAN FRANCISCO JULY 22-26 Volume 19, Number 3,1985 Finally, we discuss improvements that must be sible: the user may touch the tablet. This causes a made to current touch tablet technology, many of change to state 1. In state 1, the user is pressing on which we have demonstrated in prototype form.