A method for manufacturing an ultrasonic, flow measuring device, characterized by method steps as follows: selecting a number larger than one of straight subsections of the first signal path, which should have different distances from the measuring tube axis; establishing the distances of the straight subsections from measuring tube axis; calculating values of lengths of the straight subsections, as projected on the measuring tube axis, as a function of the number of straight subsections with the same distance from the measuring tube axis and the respective distances from the measuring tube axis; and inserting the at least a first reflection surface in the measuring tube such that the acoustic signal on the path from the first transmitter to the first receiver is so reflected on at least the first reflection surface that the first signal path comprises the straight subsections with the selected distances and the calculated values of the lengths as projected on the measuring tube axis.