HP PCL/PJL reference (PCL 5 Printer Language) - Technical Reference Manual Part I

2-4 The Page EN
PCL Coordinate System
The PCL coordinate system is defined as shown in Figure 2-2.
Figure 2-2 X,Y PCL Coordinates
The point (0,0) is at the intersection of the left edge of the logical page
and the current top margin position.
Note Since the point (0,0) is always at the intersection of the left edge of
the logical page and the current top margin position, it moves if the
top margin is changed, and rotates around the page if the orientation
is changed.