I haven't started them, and it might be a while before I do so, but I did just get used copies of Donald Knuth's books on TeX and typesetting.

Knuth is an elderly computer science better known for his more-general algorithms work, but I've been interested in pen plotting recently. Most modern font formats define areas to fill in, whuch doesn't map well to plotting. I recently discovered that MetaFont, TeX's native font format, is based on pen strokes and defining a variable width on those strokes, which is more similar to pen plotting.

Kinda dry and older books, but I've been pretty fascinated by some of the pen plotter art on Reddit, and have been looking into what the current limitations are.