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It has been noted that aviation cadet applicants sometimes pass the American Optical Company series of pseudoisochromatic plates but fail the Ishihara series. Fourteen hundred and seventyone applicants for air crew training were examined by use of the 32 plate Ishihara series, followed by the 46 plate American Optical Company series. The applicant failed if he missed 25 per cent or more of the plates in each book.
It was found that 6.6 per cent, or 100, failed the Ishihara series, and 5.7 per cent, or 83, the American Optical Company series. Only 5 of the 83 who failed the American Optical Company series could not trace the gray-blue line in plate 45 of that series, and only 13 of the 100 candidates who failed the Ishihara series did not trace the two gray-blue lines in plates 30 and 31. Fifty-seven of the 83 candidates who failed the American Optical