shake for a balance
pivot; multiply it by 2 1/4 and we obtain the thickness for the spring
detent of a pocket chronometer, which is about 1/3 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.

In any modern work on horology of value, the metric system is used.
Skilled horologists use it on account of its _convenience_. The
millimeter is a unit which can be handled on the small parts of a watch,
whereas the inch must always be divided on anything smaller than the
plates.

Equally as fine gauges can be and are made for the inch as for the
metric system, and the inch is decimally divided, but we require another
decimal point to express our measurement.

Metric gauges can now be procured from the material shops; they consist
of tenth measures, verniers and micrometers; the finer ones of these
come from Glashutte, and are the ones mentioned by Grossmann in his
essay on the lever escapement. Any workman who has once used these
instruments could not be persuaded to do without them.

No one can comprehend the geometrical principles employed in escapements
without a knowledge of angles and their measurements, therefore we deem
it of sufficient importance to at least explain what a degree is, as we
know for a fact, that young workmen especially, often fail to see how to
apply it.

Every circle, no matter how large or small it may be, contains 360deg.; a
degree is therefore the 360th part of a circle; it is divided into
minutes, seconds, thirds, etc.

To measure the _value_ of a degree of any circle, we must multiply the
diameter of it by 3.1416, which gives us the circumference, and then
divide it by 360. It will be seen that it depends on the size of that
circle or its radius, as to the value of a degree in any _actual_
measurement. To illustrate; a degree on the earth's circumference
measures 60 geographical miles, while measured on the circumference of
an escape wheel 7.5 mm. in diameter, or as they would designate it in a
material shop, No. 7 1/2, it would be 7.5 x 3.1416 / 360 = .0655 mm., which
is equal to the breadth of an ordinary human hair; it is a degree in
both cases, but the difference is very great, therefore a degree cannot
be associated with any actual measurement until the r