HUMAN FACTORS, 1967,9 (9,419-426 Readability of Dials a t Different Distances with Constant Visual Angle'

The purpose of this experiment was to strdy the readabiIity of dials at different distances when rhe visual angle subtended by rhe dials is held constant. Five dials, the sizes and markings of which were proportional to viewing distance, were tested at distances ranging from 14 to 224 in. Each of 20 subjects made 20 readings on each dial. Care was taken to select subjects with excellent uncorrected near and far visual acuity. A focus sign above each dial was used to hold accommodation time constant. Directionsto the subject stressed accuracy. Response times, errors of estimation, and questionnaire data were recorded. The results show a signifirant effect of distance on readability: Dials located at distances greater than 28 inches were read faster than two smaller, closer dials. Although there are no significant differences among rhe errors made on the five dials, the error data are consistent with the time data