"It's true enough a film speed is whatever YOU determin it to be for YOUR application, but that doesn't help a lot when your application is for 100 speed film and every 100 speed film (as "marked on the box") actually rates somewhere around 50. "(posted 8173 days ago)You should be happy. You know something that no one else knows. You know that you should set your exposure meter at 50 for VERY box of film that says 100.