Spot Color Tone Value
SCTV is a method of calibrating spot colors defined in ISO 20654-2017. This method works well with all inks and all printing methods to provide a visually linear method of calibration. It is considered to be superior to the older "TVI" method of calibration for colors that are outside of the usual process colors of cyan, magenta, yellow and cyan.
Curve4 is a commercial product that makes use of SCTV in calibrating spot colors. This replaces the "Special Inks" method used in Curve3, which was very similar.