Canon EOS-1D X Instruction Manual page 328

3 Custom Function Settings
Spot metering linked to AF point
You can enable or disable AF point-linked spot metering in the <r>
metering mode.
Center AF point only
Regardless of the AF point currently selected, spot metering will always
be linked to the viewfinder's center AF point.
Linked to active AF point
Spot metering will be linked to the manually-selected AF point. If the AF
area selection mode is set to 61-point automatic selection or Zone AF
(automatic Zone selection), spot metering is performed at the viewfinder
center.
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