A long shot. But if anybody knows the length of an 'inch' in eighteenth century Britain I will by brimming with joy! No luck on the internet.

It is for a secret project, which I will reveal next week.

Hmm...a long shot, but I seem to remember that some Parisian museum holds a metal bar that defines the exact length of a meter. Perhaps some science museums will have similar objects re: inches. Would the Greenwich Maritime museum be able to help?

Could it be the same as the old Scotish gaelic inch which was 2.554 cm or 1.0016 imperial inches.

Difficult question. I've had some of those too. It depends on when and where. A 19th century English inch is different from a 16th century Italian one. But, unless you need the exact measure, you can safely say it's approximately 2 cms.

BTW, there's a book called something like "The right measure" that deals with weights and measurements. It has little or no explanation, just the figures. It's good for European and some north African measures. I got it from Amazon.

Another option is "Weights, Money and Other Measures Used by Our Ancestors", which I believe is available online.

I have a vague memory of it being something to do with the length of one of the bones in the thumb, I think it is the last bone, i.e. the one furthest from the palm. This would go with all the other measures of the time, like the ell etc.. Yours of course may be a bit bigger, but many (but not all) people were shorter in those days and presumably had smaller bones to match

thanks people!