Comment by leoc

The "Advanced User Guide" referred to several times in the comments is The Advanced User Guide for the BBC Micro by Bray, Dickens and Holmes, 1983, ISBN 0 946827 00 1 . https://stardot.org.uk/forums/viewtopic.php?f=42&t=17242 https://archive.org/details/bbc-micro-advanced-user-guide/ I can't find a source for this now, but IIRC Bell and Braben themselves used this when writing Elite. (I am not an expert.)