Canon EOS-1DX MARK II Settings Manual page 39

A minus setting for subjects with a
long shooting distance such as soccer
provides more stable focus
The default setting is [0], which is best for shooting
su bj ect s t ha t m ov e a t s te ady speeds , o r do not
experience significant changes in speeds.
[ + 1/ + 2] are best for shooting subjects that suddenly
start or stop moving, or suddenly accelerate or
decelerate. This setting enables the camera to continue
focusing on the desired subject even when it experiences
significant, split-second changes in speed. For example,
the camera becomes less likely to focus behind an
approaching subject that moves suddenly, and less likely
to focus in front of a subject when it stops suddenly,
which would result in a blurred subject. [ + 2] can handle
greater changes in speed than [ + 1].
[ - 1/ - 2] are effective for shooting far away subjects
with small changes in speed when you want to focus
continually on a given subject, minimizing the effects of
obstructions passing by in the foreground of the shot.
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