**1. Introduction**

Escapement is a mechanism in mechanical clocks or watches, and it is considered to be one of the most important horological inventions. It transfers energy to the timekeeping element and allows the number of its oscillations to be counted [1].

> © 2016 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. © 2018 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

The detent or chronometer escapement is considered the most accurate of the balance wheel escapements and it was used in marine chronometers [1]. In 1748, Pierre Le Roy invented the early form of it. He created a pivoted detent type of escapement [2, 3]. Around 1775, John Arnold invented the first effective design of detent escapement. In 1780, Arnold's escapement was modified by Thomas Earnshaw [3, 4]. If watches or clocks had been equipped with free harmonic oscillators, they would have performed harmonic oscillations with constant frequency. But real watch balance wheels always perform dumped and driven oscillations. Thomas's modification to the chronometer escapement was very close to previously mentioned ideal [5].

Two different but equally important functions are accomplished by escapement:


Important characteristics of Thomas Earnshaw's chronometer detent escapement mechanism are:

