No more uncertainty: helps you figuring out how long that mystical short end is.

Take a pencil, a pice of paper and the film can with the short end into the darkroom/bag/tent. Feel the size of the core and mark the diameter of the short end with the pencil.

Out in the light, measure this diameter with your tape. Punch the data into and voilá, your have a good guestimate of the length: