Find the missing character?

Start on the centre left of the diagram, and move in a clockwise spiral towards the centre. Letters advance through the alphabet in steps of 2, 3, 4, etc. I.e.

A +2 = C
C + 3 = F
F + 4 = J
Similarly, Follow the pattern through the path showed in Diagram (1 to 7).
So,
Missing Character ,
M + 14 = A.