In reply to Grinning Donkey:
My understanding is he wears a camera and his wife (belaying) is sometimes somehow able to tell him whether the gear is OK or simply sitting in the crack. (Cam sizes are judged based on how much in terms of fingers and hands goes in the crack. Of course, he needs to have a good racking system for gear on his harness.) Their climbing partnership is explained I think in an earlier UKC interview; very interesting. Obviously there's a limit to how much she can really help.
I don't think there's really any other way this could be achieved. As you say, if nothing else, you need to know the gear is good, and perhaps how far up the pitch you are for phyche purposes.