Also a recognized method of testing out your 1911 after you've taken it apart and re-assembled it to make certain all safeties work and the firing pin strikes the eraser propelling the pencil.An easy and cheap way to to dry fire with instant feedback.
When I was on the 8th Army pistol team we used this method for trigger control a lot. The only difference was we'd put the dot on a piece of white paper and then tape the paper to any wall. And, yes it does work! (We used it with our .45 and .38 match weapons, the pencil didn't fit down the barrel of a .22.)