Abstract: Correction quantities are generated for yielding closer approximations of actual parameters. These are obtained by preliminarily subjecting parametric transducers to pre-selected parametric values and recording the measured values for each transducer in a data table for later use as or in correction quantities. An embodiment includes interpolation relative to data table values closest to the operationally measured parametric value and using the resulting interpolated value as a corrected parametric value. Such interpolations may be performed for two parametric transducers relative to two substances. The resulting corrected parametric values may then be subtracted to obtain a parametric difference. A further embodiment may include using correction quantities of a reference parametric transducer in interpolation calculations for the actual parametric transducers.