I recently came upon an HP 7550A Graphics Plotter. It uses the standard HPGL language, and I saw that Inkscape can save HPGL scripts. I drew a little test, and it exports fine, and with a little modification of the settings on the exporter, it plots fine, but when I use something in the Render menu, such as Spirograph or Random Tree, and all that is written to the hpgl file, is

IN;SP1;PU;

I have been having to save a svg, open it in dia, export it from dia as an hpgl, and then use hp2xx to fix dia's completely screwy coordinate output. I would love to just be able to use inkscape, as it actually works, and is nicer than dia. Any idea what my issue is?

It's been a while , but I just had this exact same problem in Inkscape and Google turned up this page. After some more fiddling I got there:

The HPGL exporter only seems to handle paths, not shapes. If I select everything and chose Path -> Object To Path then suddenly I get output that looks right in my HPGL file, instead of just the single line you describe.

Hth.