Nikon Scan User Manual page 21

Clicking this button changes the entire preview area
display (including any existing crop marquis) from
landscape to portrait orientation. The illustration on
the button changes according to the display
orientation.
Flip
The entire preview area display (including any existing
crop marquis) is flipped horizontally by clicking this
button.
The entire preview area display (including any existing
crop marquis) is flipped vertically by clicking this
button.
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