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A douzieme gauge from pre-metric times

A watchmakers "douzieme gauge" is mostly used for quick and easy measurements of the thickness of tins and diameters of shafts and screws. I mostly use them while turning a shaft, stem or pivot on my lathe. Then I don't have to check their diameters on the mikrometer. That saves me the time I otherwise would use for takeing them out of the chuck for each measurement. The advantage of the douzieme gauge: It works, even when the object in question protrudes only very little from the chuck.

The word "douzieme" derives from french, meaning "a twelfth" (douze = twelve). Meaning, you can read a fraction of a twelfth, compared with what you can read on a common millimeter rule.

Recently I found this piece in a deplorable condition at a flea market. It was so corroded, that I didn't notice it's scale was not divided in millimeters, as usual. After cleaning it at home I found a very unusually divided scale, 0-6-12-18 up to 72. I puzzled about the meaning of this scale.

After some investigatigation with my watchmaker friends, I was able to confirm that it was an old french tool. Before the metric system was introduced 1875 in Switzerland, we usually used French feet and inches as follows:

1 pied.(foot) = 12 pouces = 32.484 cm
1 pouce(inch) = 12 lignes = 2.707 cm
1 ligne(line) = 12 points = 2.256 mm
1 point = 0.188 mm


The douzieme gauge on a 1-centimeter grid, here measuring a pinion square of 6 points

The Introduction of the metric system in Switzerland:

Around the 1780s, French scientists started to experiment with a metric system, where length, volumes, weight and time could be converted easily into each other in increments of the factor 10. That resulted in the fact, that 1 kilogram water was 1 liter (at 4 degrees centigrade) corresponding with 1 cubic decimeter . And a pendulum of one meter length had a frequency of one second per swing. (Consequently, as a boy scout I used a pocket knife fixed to a one meter string as a chronograph. Boys didn't own wrist watches fifty years ago.)

On the first international metric conference 1789, the system was adopted by all the major European states, safe England and Switzerland, and was first introduced in France 1895 by the government. The first watches with 10 hour dials were sold then. (Very sought after pieces at auctions today).

And note: Even the time was made metric: One day was divided in 10 hours with each hour having 100 minutes and each minute having 100 seconds. But the 10 hour day was never accepted by the common man on the street. So the government soon went back to the 24 hours days again.

Switzerland first experimented with its own metric system, with units like feet, fingers and pounds, where a pound weighed one kilogram and a foot was exactly one third of a meter (!). Later the proper metric system was adopted on 3. July 1875.

So the puzzle of my douzieme-gauge is solved now: It is pre-1875!