Epson STYLUS PHOTO R2400 Manual page 378

You can define up to 100 paper sizes. The paper size names you
create will appear in the Paper Size list.
To delete a custom paper size, click Customize, select the paper
size from the list in the Custom Paper dialog box, then click
Delete.
Copying a pre-existing paper size to use as a template
Follow the steps below to copy an existing paper size to use as a
template.
1. Select the existing paper size to be copied and click Copy.
2. Choose either cm or inch as the Unit setting.
3. Specify the margins by typing in the Margin text boxes or by
manipulating the margins in the preview image.
4. Click OK.
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