The Uniform Chromaticity Scale (UCS) was developed to minimise the limitations of the 1931 system. It was intended to provide a perceptually more uniform colour spacing for colours at approximately the same luminance. The 1976 CIEUCS chart uses u’ and v’ coordinates. The symbols u’ and v’were chosen to differentiate from the u and v coordinates of the similar but short lived 1960 CIE-UCS system. The u’ and v’ chromaticity coordinates are also calculated from the XYZ tristimulus values according to the following formulae: