Thanks for the replies, after Lemurian's post I took a quick look on !!!!!!!!!!!!!! and this is the best illustration I could find of what he said
http://www.!!!!!!!!!!!!!!/open.file/437763/L/
It does show very clearly the scale on the AI, with the markings every 10 degrees of drift and how they line up with the HI below, with 25 degrees max deflection either side (time to go around maybe if the FPV wanders off the edge on approach??
). I couldn't find a close up with the TRK/FPA on, they're all "out the window" landing shots, but at least this shows the idea.
Thanks again for all the replies.