We show how to combine program slicing and constraint solving in order to obtain better slice accuracy. The method is used in the VALSOFT slicing system. One particular application is the validation of computer-controlled measurement systems. VALSOFT will be used by the Physikalisch-Technische Bundesanstalt for verification of legally required calibration standards. The article describes the VALSOFT slicing system. In particular, we describe how to generate and simplify path conditions based on program slices. A case study shows that the technique can indeed increase slice precision and reveal manipulations of the so-called calibration path.