1.1 ,This practice is intended as an aid for improving the accuracy of colorimetric measurements made with tristimulus colorimeters on visual display units, such as cathode ray tubes (CRTs) and self-luminous flat-panel displays. It explains a useful step in the analysis of colorimetric data that takes advantage of the fact that light from such displays consists of an additive mixture of three primary colored lights. However, it is not a complete specification of how such measurements should be made.