I loved our HP pen plotter, back in the early 1980s. I never used it for input, but one of the more useful bits of software I wrote back then was to take the ou

I loved our HP pen plotter, back in the early 1980s. I never used it for input, but one of the more useful bits of software I wrote back then was to take the output of a Coulter counter (see https://www.wikiwand.com/en/Coulter_counter https://www.wikiwand.com/en/Coulter_counter ) via some strange sort of serial interface it had (current loop?) and store it on floppy disk on a CP/M machine. I then wrote another utility to read the disk and plot parametrised graphs of it on our HP pen plotter.