This color scale was developed by Richard Hunter to provide a color scale that could be computed automatically by analog devices like those an early colorimeter would have used. The Rdab scale is an opponent-color system similar to Hunter L, a, b. Instead of an L, Rd is used to designate lightness. Sometimes Rdab is expressed as LRd aRd bRd.
Conditions for Measurement Instrumental: Most HunterLab color measurement instruments
Standard Observer Function: 2 or 10 degree
Transmittance and/or Reflectance: Either
(Formulas and Tables)
This color scale may be used for measurement of the color of any object whose color can be measured. This color scale is no longer used very often.
(See attached pdf file for the complete article with formulas and data tables)