Canon EOS-1D X Mark II DSLR Camera (Body Only) - Manual (Page 118)

3 Selecting AI Servo AF Characteristics
118
Tracking sensitivity
Sets the subject-tracking sensitivity
during AI Servo AF when an obstacle
cuts across the AF points or when the
subject strays from the AF point.
0
Default setting. Suitable for moving subjects in general.
Locked on: -2 / Locked on: -1
The camera will try to continue focusing on the subject even if an
obstacle cuts across the AF points or if the subject strays from the
AF points. The -2 setting makes the camera keep tracking the target
subject longer than the -1 setting.
However, if the camera focuses on a wrong subject, it may take
slightly longer to switch and focus on the target subject.
Responsive: +2 / Responsive: +1
The camera can focus consecutively on subjects at different
distances that are covered by the AF points. Also effective when you
want to always focus on the closest subject. The +2 setting is more
responsive than the +1 setting when focusing on the next subject.
However, the camera will be more prone to focus on an unintended
subject.
Parameters
[ Tracking sensitivity ] is the feature named [ AI Servo tracking sensitivity ]
in the EOS-1D Mark III/IV, EOS-1Ds Mark III, and EOS 7D.