Canon S450 User Manual page 109

Select inch or mm (millimeter) for the unit of measurement in the Unit box,
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and enter the desired width and height within the following ranges:
Width: 3.94" to 9.50" (100.0 mm to 241.3 mm)
Height: 3.94" to 23.0" (100.0 mm to 584.2 mm)
Click the OK button.
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Getting to Know the Windows 98/95 Printer Driver
Using the Windows 98/95 Printer Driver 109