Canon EOS-1D X Mark III Advanced User's Manual page 114

4.
Focus on the subject.
(1) Standard exposure index
(2) Exposure level mark
(3) Brighter (+)
(4) Darker (−)
Press the shutter button halfway.
The exposure value is displayed in the viewfinder and on the top LCD
panel.
To see how far the current exposure level <
exposure <
viewfinder.
>, check the exposure level indicator at right in the
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> is from standard