OK, me again. I took some time to try to sort things out with the pins and the ME lever and slide and stuff......So, it appears that the film will not be exposed (all other things being equal) if that pin cannot protrude all the way into the film back. Meaning that for the whole thing to be ready for a shot, that ME slide must not be in the way of the pin. So, without regard to the ME stuff, I have to assume that when I make an exposure, the ME "slide" is exposing the hole, and that once the exposure is complete, some mechanical device puts that ME slide back over the hole again (to prevent "ME"). Thus, if I make an exposure, do not advance the film, cock the shutter, and try to expose the film, I cannot because that pin cannot get into the back. OK. Got that. Think the logic is correct. So, assuming all parts are working properly and "dark slide maneuvers" are correct, if I make an exposure, the red flag will appear..and, now, has the ME slide moved to cover the hole? It must do that so that I don't expose that frame again. When I exposed the frame, the red flag appeared Can I then assume that when I wind the film to the next exposure, not only will the red flag be gone but the hole will be uncovered again (so that I can expose the film......?) It may be that I have major issues with simply the mechanics of the film backs regarding exposure, red flag, ME slide, etc. Is the thought process flawed? I appreciate that this is about mechanics but I need to get those under control first......