Beginning students of color and vision learn very quickly that the definition of the CIE 1931 Standard Observer was based on the observer spectral response measurements made by Wright and Guild, each working independently and using different methods. The remarkably close agreement between the two sets of data encouraged the CIE to accept the average observer color matching functions, and to establish the color notation system which has has such a vital import to communications, commerce, and industry. Although examined and reexamined many times since that time, the original data have been fully substantiated and have thoroughly withstood the tests of time and advanced experimental techniques.