Gravet Lenoir

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An unexpected strike of serendipity

Here is an unassuming wooden slide rule, missing its glass cursor. Or so I thought at first, when I bought it for a pittance from a nondescript antique shop. Later I realized that there is no wear to indicate that it ever had a cursor, and I grew suspicious. Searching the web for "Gravet Lenoir", the maker's name, revealed so little information that I had to search Usenet and write the one guy who seemed to know about this... and I learned that I had a real "find", a 19th century slide rule worth 30 times what I paid for it. The cursor, by the way, isn't missing: it hadn't yet been invented at the time!

Click photo to enlarge

Click a photo to enlarge

As you can see in the close-up, this slide rule was meticulously crafted in Paris; the address tells us that this happened sometime between 1827 and 1867. Monsieur Lenoir, a pioneer of precision slide rule manufacturing in France, was dead by then; but his partner Gravet had kept the name in order to bank on Lenoir's well-deserved reputation. In those days, you see, making precision instruments wasn't a matter of raising the capital and buying the equipment; you had to perfect your own manufacturing techniques from scratch, and a good instrument was a precious possession indeed.
This slide rule has an archaic arrangement of scales known as a "Soho" configuration: three 2-cycle logarithmic scales and a fourth single-cycle scale, with the slide bearing the same scale twice. Later slide rules would have a better arrangement, but lacking the hairline cursor, which is necessary to move readings vertically across the slide, Gravet was forced to use the system we see here.

Exhibit provenance:
I bought this item in Italy in a small antique shop that didn't specialize in technology collectables. Neither storekeeper nor customer had any idea what the old rule was worth...

More info: to learn about antique Slide Rules, join the Oughtred Society. Its journal (which is paper based) has many scholarly articles about these matters, and covers Gravet and Lenoir in its spring 2002 (Vol. 11, No. 1) issue.

An unexpected strike of serendipity