Readability of Dials at Different Distances with Constant Visual Angle

Abstract

The purpose of this experiment was to study the readability of dials at different distances when the visual angle subtended by the 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. Directions to the subject stressed accuracy. Response times, errors of estimation, and questionnaire data were recorded. The results show a significant 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 the errors made on the five dials, the error data are consistent with the time data.