Foma 100 and 400 ISO are over rated in terms of ISO. Looking at the data sheets provided by Foma both are close to box ISO with Microphen, all others fall at least one stop short. I shoot Foma 100 at 100 with Acufine, all others film I can shoot one stop higher than box speed. So I really think you need to find a way to test your film developer combo to find the working ISO for you set up, Camera, Lens, Film, Developer.