Spectrophotometric data are automatically entered on IBM punched cards by means of a Librascope Digital Readout Unit for the General Electric Recording Spectrophotometer. Conversion to color coordinates is subsequently carried out on an IBM 650 computer. The over-all precision of the spectrophotometer-digitizer-computer system corresponds to 95% confidence limits of about 0.001 in trichromatic coefficients x and y or about 0.7 NBS units of color difference (Adams chromatic value formula, normalized as in ASTM Method D1482-57T). Taking results of the National Bureau of Standards as correct, the accuracy of the average of several measurements is within 0.0005 in trichromatic coefficients or 0.4 NBS units of color difference. The error frequency of the digitizer is currently below 1 in 7000 readouts, and can be reduced to less than 1 in 200 000 readouts.
FRED W. BILLMEYER, JR., "Use of a Digital Readout Unit in Converting Spectrophotometric Data to Color Coordinates," J. Opt. Soc. Am. 50, 137-141 (1960)