Andrew,(posted 8597 days ago)"Effective speed" is the film speed setting that gives you the best quality results. With b&w film, this is almost invariably slower (more exposure) than the manufacturer recommends, whatever developer you use. Most often, following the manufacturer's recommendations delivers more contrast and less shadow detail than most experienced photographers would like to have, so after doing personal tests, most end up exposing more--much more with some films--and often developing a bit less.