Buzzybee
It may be worth looking at the preamble again - you should have 23 cells highlighted. Once you've done that, the contents (of the safe that the puzzle represents) should be apparent.
Hamish - safe to say this was a cracker of a puzzle! I thought this was very well pitched as a good challenge. Needed some different coloured highlighters to keep track of the dials, but all worked out very neatly in the end.