A Chronometer is a precision watch, which is regulated in various positions and at different temperatures and has received a certificate to that effect. This definition of a chronometer was formulated in 1951 by the Organization of Swiss Watch Manufacturers. This book gives a detailed account of chronometer testing for wristwatches in Europe, with information about testing methods, procedures, and guidelines. as well as participating makers based on Swiss Testing Agencies' yearly reports from 1925 and the Swiss Observatories' reports kept between 1941 and 1967. More than 60 chronometer wristwatches by known makers are discussed, as well as their tests. Types of errors and their possible causes will be pinpointed. Practical chronometer testing will be taught, as will the differences between chronometer and non-chronometer wristwatches from various European countries. In addition to the many photographs in the illustration section, a register listing more than 300 Swiss watch manufacturers who made chronometer wristwatches will be very useful.