How Long Is Your Cubit?

I've found another reason for Asher Benjamin's geometry lessons and the proportion diagrams on his plates.

It turns out that in 1800, the various and different measuring systems used in the western world were quite divergent. A cubit seems to have been standard measured: from your outstretched middle finger to your elbow (about 18"). But a yard might be from your finger to your nose, (36") or to your near or opposite shoulder, (30", and 42" respectively).

I think this is great, since I have been measuring with body dimensions for years - using my own body to discretely measure an interesting space without drawing attention to myself by whipping out a tape measure, or helping a client to tell me how big is 'big' by stretching out both arms and saying, "This big?"

In 1793, Napoleon tried to create a standard, a metric system, with some success. And in 1824, the English made a standard yard, also with some success. The process took a good 50 years to take hold, and today we still have lots of regional variations, not to speak of the gulf between inches and centimeters.

Here in the States people measured cloth, grain, lumber using the system they had learned in the 'old country'. A Pennsylvania carpenter who repairs 18th century houses has told me he can tell a house built by a German from one built by a Quaker by its dimensioning.

Measuring

A friend who reads this blog sent me a link to a book on tools, published by the Colonial Williamsburg Foundation, so I have requested it through inter-library loan. However, the problem with books on tools is that the authors love what the tools look like, but rarely date them. This makes it very hard for me to see how specific tools evolved.

Meanwhile I have discovered that what I'm really asking is how carpenters measured around 1800.

People didn't need uniform measurements for construction until they wanted to use interchangeable parts. If your yard was 36" and mine was 35" , it wasn't a problem.
When Asher Benjamin writes his first books, we are still making the parts for a house specifically for that house - no buying off the shelf. So when it came to finish work, each piece of moulding added at a door opening or chair rail was made to order, regardless of how it was measured.

Benjamin's introduction to geometry - his first plates - and his descriptions of how to draw the profiles of various mouldings allow his readers to adapt his patterns to their specific buildings, and use whatever measuring tools they liked.