Canon EOS M Instruction Manual page 152

3 q Changing the Metering ModeN
When One-Shot AF is set: With q, the exposure setting will be locked
when you press the shutter button halfway and focus is achieved. With w,
r, and e, the exposure setting is set at the moment of exposure. (The
exposure setting is not locked when you press the shutter button halfway.)
152
e Center-weighted average metering
The brightness is metered at the image center
and then averaged for the entire scene. This
metering mode is for advanced users.