One is an HP A3 plotter the other a very large
Calcomp...
Fun stuff.
FWIW I can create HP .PLT files for people from
Corel OCR-Trace 8 and related tools.
It can turn a hires image into an even higher one and
then do a vector conversion of the result.
(Kinda makes me want to re-create my GE
servicebureau work from 1985, where I converted
Applicon,CV and Calma Gerber out to other formats,
including Tektronix on-screen)
John A.