Abstract: A method for ascertaining a characteristic variable for evaluating a measuring arrangement comprising a clamp-on, ultrasonic, flow measuring device and a pipe, on which the clamp-on, ultrasonic, flow measuring device is secured, and/or for evaluating measurement operation of such a measuring arrangement, characterized by the method steps as follows: A) providing characteristic values relative to an exciter signal produced by the clamp-on, ultrasonic, flow measuring device; B) providing sensor-specific data as regards acoustic properties of one or more ultrasonic transducers of the clamp-on, ultrasonic, flow measuring device C) inputting data relative to the pipe material and the pipe wall thickness, especially inputting such data by a user, and D) ascertaining the characteristic variable from the parameters and data of steps A-C based on a mathematical model, as well as a computer program product and a clamp-on, ultrasonic, flow measuring device.