Optimizing a Portable Terminal Keyboard for Combined One-Handed and Two-Handed use

Human factors experimentation facilitated the design of a portable terminal keyboard for combined one-handed and two-handed operation. To ensure a comfortable grip, the terminal had to be made smaller by reducing the size of its keyboard. The product design team needed to know how small the keyboard could be before it degraded the usability of the keyboard and the overall product. The keyboard experiment was designed primarily to determine the effect of both the number of hands used in typing and key spacing on typing speed and accuracy. A total of six commercially available keyboards with key spacings varying from 0.75 to 0.45 inches were tested. Test subjects with typing skills ranging from expert to novice typed separate samples of text on each keyboard, once using one hand and once using two hands. The difference in typing speed between two and one-handed typing averaged 2—1. A key spacing less than about 0.7 inches substantially reduced typing speed but did not increase errors. Poor typists typed at roughly the same speed no matter the key spacing or number of hands used. These findings and additional human factors studies provided parameters for a keyboard smaller than standard size that is expected to allow users to achieve 90 percent of the typing speed possible on a standard size keyboard without decreasing accuracy.