Canon EOS-1D X Mark III Advanced User's Manual page 426

Setting the Initial Magnification Ratio and Position
You can set the initial magnification ratio and magnified position by selecting [
Magnificatn (apx)].
1x (no magnification)
The image is not magnified. The magnified view will start with the single-image display.
2x, 4x, 8x, 10x (magnify from center)
The magnified view starts at the image center at the selected magnification ratio.
Actual size (from selected pt)
The recorded image's pixels will be displayed at approx. 100%. The magnified view
starts at the AF point that achieved focus. If the photo is taken with manual focus, the
magnified view starts at the image center.
Same as last magnif. (from ctr)
The magnification will be the same as the last time you exited the magnified view with
the < > or < > button. The magnified view starts at the image center.
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