The Darkest Points uses code adapted from program used for Kosmos plots.
'Depth' box indicates number of points to join. Slider controls curvature of line connecting points.
PU = Pen Up. PD = Pen down. PA, Pen Absolute as opposed to Pen Relative. Coordinates are in millimetres - set up with SC0,40,0,40,2 in the initialisation line. Native resolution of HPGL is 1/40th of a millimetre.
This is copied directly to serial port of plotter as a text file.