Clear blue fertility monitor question

[Wiggy29]

Just starting to use it again, had the instruction booklet but I seem to have misplaced it during a house move. I remember the general idea but what does it mean when the 'm' comes up?

Press the m button until the m appears on the screen. This is to indicate day 1 of your cycle.

If you PM me your email address I can send you photos of the booklet pages.