Canon EOS 5DS Instruction Manual page 114

3 Selecting AI Servo AF CharacteristicsN
Parameters
Tracking sensitivity
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 enters the AF points or if the subject strays from the AF
points. The -2 setting makes the camera track the target subject
longer than with 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 when focusing on the next subject than +1.
However, the camera will be more prone to focus on the wrong
subject.
[Tracking sensitivity] is the feature named [AI Servo tracking sensitivity]
in the EOS-1D Mark III/IV, EOS-1Ds Mark III, and EOS 7D.
114
Sets the subject-tracking sensitivity
during AI Servo AF when an obstacle
enters the AF points or when the AF
points stray from the subject.