Relationship between key space and user performance on reduced keyboards.

Small computers are much in demand for mobile computing. However, keyboard size is an obstacle to further size reduction. Reducing the space occupied by keys would affect the usability of the keyboard. On the other hand, if the keys were closer together, the fingers would reach them faster. This could improve typing performance. An experiment was therefore conducted to investigate the relationship between users' performance and the center-to-center key space of reduced-size keyboards. Eighteen touch-typists were asked to do a word typing task on five different keyboards. A standard keyboard with a key space of 19.05 mm and smaller keyboards with key spaces of 16.7, 16.0, 15.6, and 15.0 mm were used in this study. No performance degradation was found on keyboards with a key space of 16.7 mm for faster typists (those capable of about 40 wpm), including those with large fingers (97.5 percentile of Japanese adult males). For faster typists with narrow fingers, there was no performance degradation on keyboards with a key space of 15.0 mm.