Expected locations of digits and letters on ten-button keysets.

Although keysets are used on a great variety of machine devices—computers, coding devices, and communications equipment— there appear to be few systematic studies concerned with the design factors that make keysets easy or hard to use. The study reported here deals with one aspect of keyset design, viz., the locations of numbers and letters on individual keys. In addition, we are concerned here with a particular class of keysets —ten-button sets used by long-distance telephone operators—but the results probably can be generalized to other practical situations. In making long-distance calls, telephone operators use a set of ten keys, arranged in two vertical rows of five, with letters and numbers on the keys as shown in Fig. 1. To complete a call, the operator usually keys a letter-number combination which looks like this: 815 RE 4-0267