Your method is a valid way to determine your personal effective film speed because it takes into consideration your shutter and lens aperture, meter and metering system, and method development. It is not a good way, however, to provide relative data useful to other users because in practice the various parts of your system could lead to exposure errors of up to one stop and even greater. In my own work I make tests for effective film speed with a carefully calibrated system that uses a light integrator to give an accuracy of exposure of 1/100 of a second. So when I compare the relative speeds of different film/developer combinations I can be sure that these comparisons are valid.
Originally Posted by Silverpixels5