kb/data/en.wikipedia.org/wiki/Chronometry-2.md

title	chunk	source	category	tags	date_saved	instance
Chronometry	3/3	https://en.wikipedia.org/wiki/Chronometry	reference	science, encyclopedia	2026-05-05T14:27:50.668059+00:00	kb-cron

The Ancient Egyptian calendars were among the first calendars made, and the civil calendar even endured for a long period afterwards, surviving past even its culture's collapse and through the early Christian era. It has been assumed to have been invented near 4231 BC by some, but accurate and exact dating is difficult in its era and the invention has been attributed to 3200 BC, when the first historical king of Egypt, Menes, united Upper and Lower Egypt. It was originally based on cycles and phases of the moon, however, Egyptians later realised the calendar was flawed upon noticing the star Sirius rose before sunrise every 365 days, a year as we know it now, and was remade to consist of twelve months of thirty days, with five epagomenal days. The former is referred to as the Ancient Egyptians' lunar calendar, and the latter the civil calendar. Early calendars often hold an element of their respective culture's traditions and values, for example, the five day intercalary month of the Ancient Egyptian's civil calendar representing the birthdays of the gods Horus, Isis, Set, Osiris and Nephthys. Maya use of a zero date as well as the Tzolkʼin's connection to their thirteen layers of heaven (the product of it and all the human digits, twenty, making the 260-day year of the year) and the length of time between conception and birth in pregnancy.

== Museums and libraries ==

=== Europe ===

There are many horology museums and several specialized libraries devoted to the subject. One example is the Royal Greenwich Observatory, which is also the source of the Prime Meridian and the home of the first marine timekeepers accurate enough to determine longitude (made by John Harrison). Other horological museums in the London area include the Clockmakers' Museum, which re-opened at the Science Museum in October 2015, the horological collections at the British Museum, the Science Museum (London), and the Wallace Collection. The Guildhall Library in London contains an extensive public collection on horology. In Upton, also in the United Kingdom, at the headquarters of the British Horological Institute, there is the Museum of Timekeeping. One of the more comprehensive museums dedicated to horology is the Musée international d'horlogerie, in La Chaux-de-Fonds in Switzerland, which contains a public library of horology. The Musée d'Horlogerie du Locle is smaller but located nearby. Other good horological libraries providing public access are at the Musée international d'horlogerie in Switzerland, at La Chaux-de-Fonds, and at Le Locle. In France, Besançon has the Musée du Temps (Museum of Time) in the historic Palais Grenvelle. In Serpa and Évora, in Portugal, there is the Museu do Relógio. In Germany, there is the Deutsches Uhrenmuseum in Furtwangen im Schwarzwald, in the Black Forest, which contains a public library of horology.

=== North America === The two leading specialised horological museums in North America are the National Watch and Clock Museum in Columbia, Pennsylvania, and the American Clock and Watch Museum in Bristol, Connecticut. Another museum dedicated to clocks is the Willard House and Clock Museum in Grafton, Massachusetts. One of the most comprehensive horological libraries open to the public is the National Watch and Clock Library in Columbia, Pennsylvania.

== Organizations == Notable scholarly horological organizations include:

American Watchmakers-Clockmakers Institute – AWCI (United States of America) Antiquarian Horological Society – AHS (United Kingdom) British Horological Institute – BHI (United Kingdom) Chronometrophilia (Switzerland) Deutsche Gesellschaft für Chronometrie – DGC (Germany) Horological Society of New York – HSNY (United States of America) National Association of Watch and Clock Collectors – NAWCC (United States of America)

== Glossary ==

== See also ==

Complication (horology) List of clock manufacturers List of watch manufacturers Winthrop Kellogg Edey Allan variance Clock drift International Earth Rotation and Reference Systems Service Time and Frequency Standards Laboratory Time deviation

== Notes ==

== References ==

== Further reading ==

Perman, Stacy (2013). A grand complication: the race to build the world's most legendary watch. New York: Atria. ISBN 978-1-439-19008-1. Berner, G.A., Illustrated Professional Dictionary of Horology, Federation of the Swiss Watch Industry FH 1961 - 2012 Daniels, George, Watchmaking, London: Philip Wilson Publishers, 1981 (reprinted June 15, 2011) Beckett, Edmund, A Rudimentary Treatise on Clocks, Watches and Bells, 1903, from Project Gutenberg Grafton, Edward, Horology, a popular sketch of clock and watch making, London: Aylett and Jones, 1849 IEEE Guide for Measurement of Environmental Sensitivities of Standard Frequency Generators (Revision of IEEE Std 1193 - 1994), Piscataway, NJ: IEEE, doi:10.1109/ieeestd.2004.94440, ISBN 0-738-13711-1 IEEE Standard Definitions of Physical Quantities for Fundamental Frequency and Time Metrology—Random Instabilities, Piscataway, NJ: IEEE, doi:10.1109/ieeestd.2008.4797525, ISBN 978-0-738-16855-5