The C.Fn III - 10 custom function controls how the focus points are displayed.
In Manual Focus
0: Enabled. When you have focus in Manual mode, the focus confirmation indicator will be the same as with AF.
1: Disabled. There’s never a focus confirmation through any indicator.
In AI Servo Focus
0 — Enabled. This only applies to the Zone AF and 19-point AF (doesn’t apply to single point or expansion point.) The displayed focus point will track the subject within the selected Zone AF or with the 19-points AF.
1 — Disabled. The display of the focus point will not track the subject within the selected Zone AF or the 19-points AF.
- This only applies to the display of the focus point. It’s not the tracking of the subject.
- I really don’t like that Canon sets 0 to enabled and 1 to disabled. In the computer world, 0 = false = disabled and 1 = true = enabled.