An Analysis of the Lever Escapement

From the author…Before entering upon our subject proper, we think it advisable to explain a few points, simple though they are, which might cause confusion to some readers. Our experience has shown us that as soon as we use the words millimeter and degree, perplexity is the result. What is a millimeter? is propounded to us very often in the course of a year; nearly every new acquaintance is interested in having the metric system of measurement, together with the fine gauges used, explained to him. The metric system of measurement originated at the time of the French Revolution, in the latter part of the 18th century; its divisions are decimal, just the same as the system of currency we use in this country.

A meter is the ten millionth part of an arc of the meridian of Paris, drawn from the equator to the north pole; as compared with the English inch there are 393708⁄10000 inches in a meter, and there are 25.4 millimeters in an inch.

The meter is sub-divided into decimeters, centimeters and millimeters; 1,000 millimeters equal one meter; the millimeter is again divided into 10ths and the 10ths into 100ths of a millimeter, which could be continued indefinitely. The 1⁄100 millimeter is equal to the 1⁄2540 of an inch. These are measurements with which the watchmaker is concerned. 1⁄100 millimeter, written .01 mm., is the side shake for a balance pivot; multiply it by 2¼ and we obtain the thickness for the spring detent of a pocket chronometer, which is about ⅓ the thickness of a human hair.

The metric system of measurement is used in all the watch factories of Switzerland, France, Germany, and the United States, and nearly all the lathe makers number their chucks by it, and some of them cut the leading screws on their slide rests to it.