Canon EOS 1 Instructions Manual page 31

AE Lock
-You can remove your thumb from the AE
lock button if you keep the shutter button
pressed
halfway.
Exposure will be locked
at the value displayed in the viewfinder and
on the display panel.
3) Press the shutter button all the way to take
the picture.
-After the picture has been recomposed,
both the current and the locked exposure
values appear in the viewfinder on the right
side in the exposure scale.
-See p. 69 for an explanation of all viewfinder
data.
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