I load forty frames to get a thirty six exposure roll.

If you are careful as you handle the film, so as not to pull out too much extra film when loading a cartridge and you are conservative with pulling out too much leader when loading the camera, you can get thirty five or thirty six clean exposures. I usually get thirty four plus one "maybe" exposure at the end of the roll.

This, I don't mind because I often scan my film for proofing purposes and for display on computer/Internet. The clear frame at the beginning of the roll and the black frame at the end gives me the light/dark references from which to adjust my scanner. Once I have those two references set, I can batch scan the whole roll in about half the time it would take to do every frame individually.

i don't mind giving up a frame or to if I can have a benefit later on.