The Explorers Guide to the ZX81 - Mike Lord PB 1982 Timedata Computers

Basic Electricity: An Introductory Programmed Instruction Training Course:

A Programmed Course In Basic Electricity, New York Institute of Technology 1963

Gateway Guide to the ZX-81 and ZX-80 by Mark Charlton Sinclair

A Programmed Course Basic Transistors

I Wish I Knew About The Spectrum and ZX81 Jonathan Chapple Book 1983 Retro

Getting Acquainted With Your ZX81 Sinclair Computer Tim Hartnell 3rd Edition

Programming in BASIC a beginners course 1975 BASIC computing history RARE