I bought a 1 foot chesterman rule from Chesterfield market a couple of weeks ago. I am a Sheetmetal-worker by trade, (industrial units Sheffield off the wicker) and progressed to business owner, over 40 yrs, and remain proud of my heritage and trade, from this Great Steel city. All the tools from my youth were made in Sheffield and were the best around, not like some of the crappy stuff today, and if I see it in the flea markets I buy it, hence my Chesterman 1 foot. I too was shocked when I put my Stanley tape on it, and was mystified, as it’s the real McCoy, then noticed the 1/30 & 1/40 No 1324D !! Anyway, I will check with the guys at kelham island, but think one of your bloggers may be right, it could be a pattern makers rule to take account of shrinkage of different materials, and hope to find that out. My point is though, The old masters of Sheffield tooling were very very right boys, and in my opinion deserve MASSIVE credit for quality and manufacturing techniques, that led the world, sadly dismissed in the rose tinted glasses of the computer/robotic world of today, and derided by as dirty factory jobs, by those who don’t have a clue of the skill or brain power involved. MASSIVE respect to our forefathers !!!