Effects of Key Size and Spacing on the Completion Time and Accuracy of Input Tasks on Soft Keypads Using Trackball and Touch Input

Simulated keyboards on touch screens are becoming the norm for data entry on mobile and kiosk systems. Since onscreen keyboards compete with other user interface elements for limited screen space, it is essential that soft keyboard designs are optimally laid out. This paper describes an experiment in which the performance and accuracy of data input on soft keyboards with square keys of two different widths (10 and 15 mm) and two inter-key gap distances (1.5 and 4.5 mm) were evaluated. Three methods of input were studied: finger, stylus, and trackball. Entry times were the shortest and most accurate for stylus touch, although trackball input was the most accurate for the smallest key size. The spacing between keys did not exhibit a significant effect regardless of key size and input method. A key size of 15 mm appears to be sufficiently large to provide acceptable accuracy for touch input, although a key size of 10 mm was equally acceptable for trackball input.