Like with film speed calculation, what is considered the minimum useful gradient, while determined using a flare free test, has been adjusted to reflect the affects of flare.
Originally Posted by Michael R 1974
In my opinion most of the testing methods are more about producing a range of EIs that reflects the author's personal taste, whether it's about having enough of a safety factor, or producing enough shadow contrast, or producing a negative that works in conjunction of the just black printing test. For all but specialty developers, speed testing isn't really all that necessary and with specialty developers a simple comparison is between the two developers is all that is really required. It's more important to personalize the way the photographer likes to expose (personal EI) and that can be determined using the ISO speed as a foundation.
I believe one of the reasons why there's such a fixation on speed determination is that with simplified Zone System method of sensitometric testing, you don't produce a curve, but only two points of density. In order to determine the contrast, you first need to find the base point. This is backwards from general sensitometric testing. There the film is exposed and developed to differing degrees. The contrast is then determined along with the effective film speed for that contrast. Has the simplification involved in such methods as the Zone System unintentionally overemphasized the importance of speed and a speed point and under emphasized of the importance of contrast determination? There seem to be far more discussions on speed and how to test for it then there are about contrast.