The adjustable parameters in a MacAdam-modified version of Friele’s 1965 proposal for calculating color differences have been optimized, according to a criterion of MacAdam, to fit PGN experimental data. The mean-square error of fitting is 0.030. The distribution of the resulting color-metric coefficients more closely approximates those of the PGN data than do previous versions of Friele's proposals. The optimized primaries have chromaticity coordinates of x=0.74054, y= 0. 2 5946 for the red; x= -1.11696, y=2.11696 for the green; and x=0.13939, y= -0.03454 for the blue primary.
K. D. CHICKERING, "Optimization of the MacAdam-Modified 1965 Friele Color-Difference Formula," J. Opt. Soc. Am. 57, 537-540 (1967)