Fair point Ivor, but it is generally considered that the main manufacturers ran the census numbers in sequence with the frame numbers. But nothing of course is cast in stone. I found this out with one on my Velo's, where I calculated the census number in sequence, but then found out from the VOC that the factory ledgers show my number to be out by 11. But then there are quite a few anomalies with Velocette, who did a few things not quite according to the book. Ron