On the M3, I used the entire viewfinder. On the M6 I use the 35 lines. My grandson, in his ultimate wisdom, filed the CV 40 to bring up the 35 lines on the M6. I've yet to try it on the M8, and, as he is not close enough to wrap my hands around his neck and squeeze, I will wait and see.
Everyone has a photographic memory, but not everyone has film. ~Author Unknown