"M" was a 50 millisecind delay in shutter opening from the time the contacts closed, sending electricty to the "M" class flash bulb. The bulbs would take abouit 50 milliseconds to reach the appropriate light output, and the shutter would open.

"X" was no delay - electronic flash was *much* faster - so no delay ws required or wanted.

"V" was the self-timer - normally, the shutter would be triggered about ten seconds after the shutter relaese was pressed.