A super fun book about what you would need to know if your time machine crashed in the distant past before most stuff was invented. It’s flow-chartish covering topics like metallurgy and agriculture with a bunch of fun appendices about how to do specific things. The whole tone is a very wry “Whoops, sorry you got stranded. Well here’s what you’ll need to do to stay alive and.or make inventions from scratch” and is delightful to read.