A new high precision, tristimulus, filter colorimeter suitable both for research and for industrial use has been developed. The instrument can reproducibly measure CIE tristimulus values X, Y, and Z, and ratios of tristimulus values, sample to standard, to four significant figures for most colours. Colour differences considerably smaller than those which a trained observer can visually detect can be measured on all colours from whites to blacks of about density 4. The luminous apparent reflectance of carefully polished black glass has been measured as 0.012%. Tables of values functions and alignment charts have been prepared which permit rapid conversion of instrumental measurements into colour coordinates of coordinate differences of equal visual spacing in a modified Adams chromatic value system.
