Published in 1967, this is a detailed guide for constructing a model of a digital computer using basic electrical components (switches, wire, batteries) and hardware store items. The machine doesn't operate by itself - the person operates it by flipping switches, turning dials, etc. according to a set of defined rules.
I found this book at the public library some time around 1978, and it became the template for my grade eight science fair project. I was mesmerized by the vision of how one of these machines *really* worked. This book teaches the hardcore details of computer architecture, to a depth one generally doesn't see any more.
The catalog at my library no longer lists the book, and I haven't seen a physical copy of it in decades. Persistent Internet searches turned up a PDF, and I enjoyed flipping again through pages of construction diagrams, explanations of boolean algebra, truth tables, numbering systems, etc. Fun, geeky stuff.