The Physikalisch-Technische Bundesanstalt must check all measurement instruments requiring calibration. Since almost every measuring instrument is controlled by software today, it must be guaranteed that the data path from the sensor input to the display (calibration path) cannot be influenced by external factors. The VALSOFT tool detects, analyzes and visualizes influences on the calibration path. The analysis is based on Program Slicing and Constraint Solving. For any program point (e.g. outputs of measured values) those statements can be determined, which influence this point (so-called Slice). Additionally. exact conditions on which suspicious data flows take place can be calculated (so-called path conditions). Applications within other safety-critical areas arc possible.