Day 4 of the learning challenge and I'm playing around more with the Zeus / Monitor and Disassembler environment and learning about addition on 8-bit machines. One thing that finally crystallized for me was how registers (which are 8-bits in length) could hold larger numbers like addresses (answer: use two registers. Duh.) So registers like B and C can be combined together to form BC (which can contain a 16 bit number spread over two 8-bit registers. This is something I learned a while ago bit it really hit home with me with the explanations in the ZX Spectrum Machine Code books. There's also the concept of carry bits which I hadn't understood until recently.I'm still a little fuzzy on the differences between ADC and ADD so I'll work on re-reading that section tomorrow. But for now I'm pretty pleased with my progress.