Editing Clock (section)

===Oscillator===

[[File:Floating Balance Escapement.gif|thumb|[[Balance wheel]], the oscillator in a mechanical [[mantel clock]]. ]]

The timekeeping element in every modern clock is a [[harmonic oscillator]], a physical object ([[resonator]]) that vibrates or oscillates repetitively at a precisely constant frequency.<ref name="Marrison" /><ref name="Mondschein">{{cite book
 | last1  = Mondschein
 | first1 = Kenneth
 | title  = On Time: A History of Western Timekeeping
 | publisher = Johns Hopkins University Press
 | date   = 2020
 | page  = 88
 | isbn   = 978-1-4214-3827-6
 }}</ref><ref name="Britannica">{{cite encyclopedia
  | title = Mechanics: Simple harmonic oscillations
  | encyclopedia = Encyclopedia Britannica online
  | date = 2020
  | url = https://www.britannica.com/science/mechanics/Simple-harmonic-oscillations
  | access-date = 4 January 2023}}</ref><ref name="Bloomfield">{{cite book
 |last1        = Bloomfield
 |first1       = Louis
 |title        = How Everything Works: Making Physics Out of the Ordinary
 |publisher    = Wiley
 |date         = 2007
 |page        = 296
 |url          = https://books.google.com/books?id=_ZNxDwAAQBAJ
 |isbn         = 978-0-470-17066-3
 |access-date  = March 19, 2023
 |archive-date = April 4, 2023
 |archive-url  = https://web.archive.org/web/20230404215125/https://books.google.com/books?id=_ZNxDwAAQBAJ
 |url-status   = live
}}</ref>
* In mechanical clocks, this is either a pendulum or a [[balance wheel]].
* In some early electronic clocks and watches such as the [[Accutron]], they use a [[tuning fork]].
* In [[quartz clock]]s and watches, it is a [[crystal oscillator|quartz crystal]].
* In [[atomic clock]]s, it is the vibration of electrons in atoms as they emit microwaves.
* In early mechanical clocks before 1657, it was a crude balance wheel or [[Verge escapement|foliot]] which was not a harmonic oscillator because it lacked a [[balance spring]]. As a result, they were very inaccurate, with errors of perhaps an hour a day.<ref>Milham, 1945, p. 85</ref>
The advantage of a harmonic oscillator over other forms of oscillator is that it employs [[resonance]] to vibrate at a precise natural [[resonant frequency]] or "beat" dependent only on its physical characteristics, and resists vibrating at other rates. The possible precision achievable by a harmonic oscillator is measured by a parameter called its [[Q factor|Q]],<ref>{{cite web|title=Quality factor, Q|work=Glossary|publisher=Time and Frequency Division, NIST (National Institute of Standards and Technology)|year=2008|url=http://tf.nist.gov/general/enc-q.htm|access-date=2008-06-04|archive-url=https://web.archive.org/web/20080504160852/http://tf.nist.gov/general/enc-q.htm|archive-date=May 4, 2008}}</ref><ref>{{cite book| url = https://books.google.com/books?id=Z7chuo4ebUAC&pg=PA44| title = Jespersen 1999, pp. 47–50| isbn = 978-0-486-40913-9| last1 = Jespersen| first1 = James| last2 = Fitz-Randolph| first2 = Jane| date = January 1999| publisher = Courier Corporation| access-date = November 6, 2015| archive-date = July 3, 2023| archive-url = https://web.archive.org/web/20230703114215/https://books.google.com/books?id=Z7chuo4ebUAC&pg=PA44| url-status = live}}</ref> or quality factor, which increases (other things being equal) with its resonant frequency.<ref>{{cite book|last=Riehle|first=Fritz|title=Frequency Standards: Basics and Applications|publisher=Wiley VCH Verlag & Co.|year=2004|location=Germany|page=9|url=https://books.google.com/books?id=WZ34pQV-DXMC&q=Q+linewidth+%22split+the+line%22&pg=PA9|isbn=978-3-527-40230-4|bibcode=2004fsba.book.....R}}{{Dead link|date=February 2024 |bot=InternetArchiveBot |fix-attempted=yes }}</ref> This is why there has been a long-term trend toward higher frequency oscillators in clocks. Balance wheels and pendulums always include a means of adjusting the rate of the timepiece. Quartz timepieces sometimes include a rate screw that adjusts a [[capacitor]] for that purpose. Atomic clocks are [[Standard (technical)|primary standards]], and their rate cannot be adjusted.

====Synchronized or slave clocks====

[[Image:Greenwich clock 1-manipulated.jpg|thumb|The [[Shepherd Gate Clock]] at the [[Royal Observatory, Greenwich]] receives its timing signal from within the [[Royal Observatory, Greenwich]].]]

Some clocks rely for their accuracy on an external oscillator; that is, they are automatically synchronized to a more accurate clock:
* [[Slave clock]]s, used in large institutions and schools from the 1860s to the 1970s, kept time with a pendulum, but were wired to a [[master clock]] in the building, and periodically received a signal to synchronize them with the master, often on the hour.<ref>Milham, 1945, pp. 325–328</ref> Later versions without pendulums were triggered by a pulse from the master clock and certain sequences used to force rapid synchronization following a power failure.
[[File:Telechron clock 2H07-Br Administrator.JPG|thumb|Synchronous electric clock, around 1940. By 1940 the synchronous clock became the most common type of clock in the U.S.]]
* Synchronous electric clocks do not have an internal oscillator, but count cycles of the 50 or 60 [[Hertz|Hz]] oscillation of the AC power line, which is synchronized by the utility to a precision oscillator. The counting may be done electronically, usually in clocks with digital displays, or, in analog clocks, the AC may drive a [[synchronous motor]] which rotates an exact fraction of a revolution for every cycle of the line voltage, and drives the gear train. Although changes in the grid line frequency due to load variations may cause the clock to temporarily gain or lose several seconds during the course of a day, the total number of cycles per 24 hours is maintained extremely accurately by the utility company, so that the clock keeps time accurately over long periods.
* Computer [[real-time clock]]s keep time with a quartz crystal, but can be periodically (usually weekly) synchronized over the [[Internet]] to atomic clocks ([[Coordinated Universal Time|UTC]]), using the [[Network Time Protocol]] (NTP).
* [[Radio clock]]s keep time with a quartz crystal, but are periodically synchronized to [[radio time signal|time signals]] transmitted from dedicated [[Radio clock#List of radio time signal stations|standard time radio stations]] or [[satellite navigation]] signals, which are set by atomic clocks.