Abstract: A coefficient generator, data processing system and method of data reduction in correspondence with multiple-term parametric relationships, and particularly provides for data reduction in correspondence with approximative descriptions which include multiple dependent-variable terms whose higher order derivatives do not vanish. Forms of inverse of deviation variations are implemented to provide weighting which will correct for nonlinear function variations. The forms of inverse deviation weighting are implemented for representing forms of residual weighting and forms of implied squared residual weighting. Represented phases of function similation establish adept equations and implement forms of data processing and representing. Adept data processors correspondingly provide for characterizing approximating relationships in correspondence with provided data.