HP Color LaserJet 8550 Multifunction Printer series - Manual (Page 188)

EN Print Quality Problems 187
Print Quality Problems
Unless otherwise specified, all references in this section to horizontal
or vertical directions of print quality problems refer to problems found
on letter- and A4-sized media. These media sizes are fed into the
printer long edge first.
Because media sizes other than letter or A4 are fed into the printer
short edge first, the orientations of print quality problems are the
opposite of those on letter or A4-sized media. Print quality problems
that appear horizontally on a letter- or A4-sized page when it is held
with the short edge up will run vertically on other media sizes when
the page is held with the short edge up. The same is true for a vertical
defect on a letter- or A4- sized page: it will appear as a horizontal
defect on other sizes of media.
The following figure shows a print quality problem printed on both a
letter- or A4-sized page and the same defect on an 11-by-17 inch or
A3-sized page (or any other size of media).
Figure 17
A Letter- or A4-sized media
B 11-by-17 inch or A3-sized media (or any other size of media)
C Print quality problem
D Direction media moves through printer