The measurement system transfer characteristic is an unsteady, nonlinear function that depends upon time and ambient conditions. The article presents a method of tracking the real characteristic by using periodic autocalibration of the real characteristic and by applying a tangent method to the ideal characteristic. The efficiency of the algorithm has been verified for dc current generation. Periodic autocalibration fixes the current state of the measurement system characteristic by measuring internal references. The correction of a quantity at the input of the current generator is calculated from measurement of its output quantity and by using a tangent method applied to the ideal current generator characteristic. ©1996 American Institute of Physics.