Epson EcoTank Pro ET-5150 Wireless All-in-One Supertank Printer - Manual (Page 187)

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You see a screen like this:
3. Select an option for the Scan area setting, if necessary.
Note: The Scan area setting limits the scan area to a selected size starting at the placement arrow
on the scanner bed. It does not scale the image to the selected size.
4. Select SCAN .