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.