I suppose there's as much credence in an amateur saying things in a jokey manner [thank the Gods!!] as in the words of a dusty old man reading from a lectern nowadays. He could have said "One must erect a light-proof shelter of some description over each stone in turn, using a regulation 500Kw lamp, held obliquely to the stone surface, progressing from stone to stone in turn" but I'd have skipped it for the next post before I got halfway through ;)