Chord keyboards.

Unlike the standard typewriter keyboard, keying on a chord keyboard is carried out by simultaneous patterned pressing of one or more keys. This results in fewer keys being needed on a chord keyboard when compared with a sequential keyboard, where keys are pressed one at a time. For example, five keys allow a total of 31 (2(5) - 1) different chord combinations to be generated. The feasibility of using a chord keyboard as a data entry input device was first seriously investigated in the mid-1950s by the Canadian Post Office. The trend towards research into chord keying reached a peak around 1960 when International Business Machines (IBM) studied two chord keyboards to rival the typewriter. It was not until the 1970s that chord keyboards became commercially available and within the last decade three chord keying devices have been marketed. The emphasis on the development of these recent keyboards has moved from task specific to more general purpose applications. This paper (based upon Martin (1980) the author's maiden name) reviews the chord keyboards which have been developed since the 1940s with special emphasis on the mail sorting application, and draws some conclusions concerning future developments.