I open this from time to time when I forget the diagonal of a format, etc. It shows the film area and diagonals for the basic formats. I first did this some years ago and I believe I used the frame on film measurements from exposed images on my own equipment so it may not be at an accepted standard but should serve as a good general reference. Please point out any errors you spot as this wasn't meant for "prime time" but just a handy, quick reference for my own use. Maybe some panoramics would be interesting to add for calculating an "ideal" enlarging lens focal length, etc?