We introducean experimental calibration method for force transducers with interferometric readout. The head of the transducer iscompressed onthe panofaweighing scale until the first maximum of interference isreached. An optomechanical feedback loop makes sure that the force applied remains constant during the integration time of the weighing scale. At the end of the integration time, the transduceris forcedto moveto the next maximum of interference, where it isagain locked into position to allow the user to read the corresponding increase in weight on the scale. Repeating a similar procedure for a series of consecutive maximum-to-maximum steps, one canfinally plot the weight indicated by the scale as a function of the displacement of the head of the transducer, and, from there, extract its spring constant. The method relies only on measurements ofweights and laser wavelengths, both of which can be, in principle, referred to metrological standards.