You can express coordinates along the X and Y axes using two types of units: plotter units and user units.
Plotter units
The plotting area is divided into plotter units with 1016 plotter units per inch, 40 plotter units per millimetre. The printer converts the number of plotter units to equivalent dot coordinates. Since the printer prints in dots per inch, a scale factor is used. This yields a plotted image that is as close as possible to the image that would be achieved on the plotter.
User units
User units allow you to use the Scale command to redefine the size of units along the x and y axes and to customise the coordinate system to suit your needs.
The plotting grid is a two-dimensional Cartesian coordinate system. In normal orientation, the origin point (0,0) is at the lower-left corner of the imageable area of the page. The left edge of the imageable area is the y axis and the bottom edge is the x axis. When rotation is enabled (RO command), the origin point rotates to the upper-left corner of the imageable area.
Picture presentation directives are a group of commands which are used to define a bounding rectangle to contain the HP-GL/2 image and to determine a scaling factor for enlarging or reducing it. The position of the upper-left corner of the bounding rectangle is determined by the anchor point.
The area on the page where a vector graphics image can be printed, is determined by the effective window, which is the intersection of the following four boundaries:
Hard-clip limit
The hard-clip limit refers to the boundaries resulting from the physical limits of the printer (identical to the printable area in PCL mode).
Soft-clip limit
This refers to the area defined with the IW command.
Logical page
The logical page defines the area where the cursor can be positioned. The cursor refers to the location on the page where the next character will be positioned, using the commands from the Vector group.
PCL picture frame
The default initial scaling points and input window.