Quite possibly the best book available on 6502 programming for the BBC Micro. Ian Birnbaum is an excellent teacher here, paring everything back and explaining how 6502 sits alongside BBC BASIC and how the 8-bit architecture of the machine works in practice. I learnt so much from this book and it gave me an appetite to learn more and apply it to my own programming. Highly recommended for anyone embarking on 6502 for the first time.