Nikon aperture priority cameras (such as the KM, EM, and others) had the "feature" that the meter would peg and refuse to budge is you chose an aperture outside of the allowable range for a particular film speed. This was poorly documented and often causes confusion.

When I first purchased a used EM, I thought the meter was behaving erratically and almost sent it in for repair.

Another feature with some Nikons is that the meter will not turn until two or more frames have been wound off to get past the film leader.