There is another way to fool the camera. In Cason Graves book, "Zone System for 35mm" (not sure if that is the exact title) he shows how by using either metalic or black plastic tape you can cover the different parts of the code on the canister to make the camera expose the film to your specifications. He has a table that shows what parts to alter to change exposure of a 400 speed to 200, 100 to 50 etc. I would imagine that somewhere on the web there is a site or individual that has the information available.