The effect of keypad angle of a table keyphone on keying performance

Two keypad angle experiments, one numeral legibility experiment and one button-tapping rate experiment are described. The effects of keypad angle on keyphone positioning, keying time, keying errors and on a keying performance measure are discussed. A geometrical method for estimating optimum keypad angle is introduced. It is concluded that the optimum angle for a keypad depends on its height above the desk surface. The geometrical method can be used to estimate the best anglein the absence of experimental evidence. For the experimental keyphone (keypad height about 90 mm) the best keypad angle was found to be about 25 degrees to the horizontal, but the effect of a 10 degrees deviation either way from this angle was quite small.