A railroad chronometer or railroad standard watch is a specialized timepiece that once was crucial for safe and correct operation of trains in many countries. A system of timetable and train order, which relied on highly accurate timekeeping, was used to ensure that two trains could not be on the same stretch of track at the same time.
Regulations of the watches used by critical personnel on the railroads (engineer, conductor, switch yard controllers, etc.) were specified almost from the beginning of widespread railroad use in the 1850s and 1860s. These regulations became more widespread and more specific as time went on, with some watches that were "railroad standard" at an earlier time eventually becoming obsolete as technology improved. There was, however, no absolute, universal definition used across different railroad lines. Each company appointed one or more "time inspectors" (typically a watchmaker) who decided which watches were acceptable for use. In the United States, the American Railway Association held a meeting in 1887, which resulted a fairly standardized set of requirements, but not all railroads adopted them.
One notable watch inspector was Webb C. Ball. His first job as a time inspector was when he was brought in by the Lake Shore and Michigan Southern Railways in 1891 after a crash and was tasked with bringing their time inspection standards up to industry normals. Ball's career eventually led to his being the time inspector on more than half the United States' railways, leading to a far more uniform set of standards in the U.S.
A typical railroad's requirements for a watch in the early 20th century might include:
The minimum requirements were raised several times as watch-making technology progressed, and the watch companies produced newer, even more reliable models. By World War II, many railroads required watches that were of a much higher grade than those made to comply with the original 1891 standard.
The Waltham Watch Company and the Elgin Watch Company were both used as early as the 1860s and 1870s  as railroad standard watches. Later, Hamilton Watch Company, Illinois Watch Company and many of the other American watch manufacturers all produced railroad-grade watches.