HP Color LaserJet 8550 Multifunction Printer series - Manual (Page 89)

EN
Enlarging or reducing originals 89
Using Zoom mode
The sizes of the original and the copy media can be entered in 1 mm
or 1/16 in increments using a number entry screen on the display
panel. Once you have entered the sizes, the copy module calculates
the copy ratio using the following formula:
[copy ratio (%) = copy size (mm or in) / original size (mm or in)] x 100
If the calculated copy ratio is smaller than 25%, it will be set to 25%. If
the ratio is larger than 400%, it will be set to 400%.