The language is formed from a series of two letter codes, followed by optional parameters. For instance an arc can be drawn on a page by sending the string:
This means Arc Absolute, and the parameters place the center of the arc at 100,100 on the page, with a starting angle of 50 degrees measured counter-clockwise. A fourth optional parameter (not used here) specifies how far the arc continues, and defaults to 5 degrees.
Typical HPGL files started with a few setup commands, followed by a long string of graphics commands. For instance:
|IN;||initialize, start a plotting job|
|IP;||set the initial point (origin), in this case the default 0,0|
|SC0,100,0,100;||set the scale so the page is 0 to 100 in both X and Y directions|
|SP1;||select pen 1|
|PU0,0;||move pen to starting point for next action|
|PD100,0,100,100,0,100,0,0;||put down the pen and move to the following locations (draw a box around the page)|
|PU50,50;||lift the pen and move to 50,50|
|CI25;||draw a circle with radius 25|
|SS;||select the standard font|
|DT*,1;||set the text delimiter to the asterisk, and don't print them (the 1, meaning "true")|
|PU20,80;||lift the pen and move to 20,80|
|LBHello World*;||draw a label|
The coordinate system was based on the smallest units one of their plotters could support, and was set to 25 µm (i.e. 40 units per millimeter, 1016 per inch). The coordinate space was positive or negative floating point numbers, specifically ±230.