HP Laserjet 1200 - Manual (Page 19)

EN Identifying the printer’s components 17
Printer media guides
Both input trays have side media guides. The main input tray also
has a rear media guide. Media guides ensure that the media is
correctly fed into the printer and that the print is not skewed
(crooked on the media). When loading media, adjust the media
guides to match the width and length of the media that you are
using.