The steps do not differ by a constant factor, so you cannot use it the way you would use a calibrated step wedge. In fact, the quad curve that was used to make the negative has intentionally made the steps uneven in order to compensate for the nonlinearity of the process, which has an “S” shaped characteristic curve. For example, if the shadows of the image would have printed too dark, the curve has increased the ink densities in the higher-numbered cells in order to lighten the shadows in the print.
Keith Schreiber actually found out a way to create a calibrated step wedge using the Piezography Professional Edition v2 tools. He posted about it here.