When I wrote my book "Crafting Interpreters", I hand-lettered every single word in every illustration separately so that it would be as imperfect as it appeared.
The only works of comparable quality I am aware of are classics like the Moosewood Cookbook[0] (famously completely hand typeset), Allen and Mikes Really Cool Backcountry Ski Book[1], and Anybody's Bike Book[2].
Hand illustrating technical content is so much better than sterile diagrams, and it lends a sense of personalization, especially if the illustrator is also the author, which is a rarity.
[0] https://www.baumanrarebooks.com/rare-books/katzen-mollie/moo...
Good lord, I'm going to think about this every time I consider dedication to craft.
Seriously, wow. That's impressive. I'm sorry this isn't more substantive of a comment, but I really wanted you to know how amazing that is (as you probably already do).
Also, lettering was sort a of a nice peaceful zen break from the harder work of writing prose.