A Comparison of Inter-Symbol Contrast Ratios for Segmented Digital Readouts.

Twelve subjects viewed a Chicago Miniature segmented digital readout display to compare symbol legibility under two inter-symbol contrast ratio conditions - 41 and 21. Using two test lamps designated A and B, a series of test trials was presented under both conditions randomly intensifying the three horizontal segments of symbol A to determine the effect, if any, on symbol legibility. The stimuli consisted of numerical digits digits 3, 5, and 9 were presented at symbol A and digits 0-9 at symbol B. Performance data were based on subjects digital readout error scores. From evaluation of the performance data, it was concluded that the 41 inter-symbol contrast ratio was significantly better than the 21 condition and that there was no apparent aural effect degrading performance under either condition. Additionally five was significantly misidentified more often--primarily as a nine. This identification error was attributed to insufficient distinguishing cues between the two digits. Author