Canon EOS-1D C Instruction Manual page 87

Case 6: For subjects that change speed and move erratically
Default settings
• Tracking sensitivity: [0]
• Accel./decel. tracking: [+1]
• AF pt auto switching: [+1]
If the speed of the moving subject suddenly changes greatly, setting
[Accel./decel. tracking] to [+2] may give better results (p.89).
If the subject moves suddenly and erratically up, down, left, or right,
setting [AF pt auto switching] to [+2] may give better results (p.90).
3 Selecting AI Servo AF Characteristics (For a Subject)
Geared for tracking moving subjects
whose speed can change dramatically
and suddenly. Also, if the target subject
moves dramatically up, down, left or right
and it is difficult to focus, the AF point
switches automatically to track the
subject.
This setting takes effect when the
following AF area selection modes are
set: AF point expansion (Manual
selection
(Manual selection, surrounding points),
Zone AF (Manual selection), 61-point
automatic selection AF.
This setting is not available with the
Single-point Spot AF (Manual
selection) and Single-point AF
(Manual selection) modes.
), AF point expansion
87