Editing Radio clock (section)

====Clock receivers====
A number of manufacturers and retailers sell radio clocks that receive coded time signals from a radio station, which, in turn, derives the time from a true atomic clock.

One of the first radio clocks was offered by [[Heathkit]] in late 1983. Their model GC-1000 "Most Accurate Clock" received shortwave time signals from radio station [[WWV (radio station)|WWV]] in [[Fort Collins, Colorado]]. It automatically switched between WWV's 5, 10, and 15&nbsp;MHz frequencies to find the strongest signal as conditions changed through the day and year. It kept time during periods of poor reception with a quartz-crystal [[oscillator]]. This oscillator was disciplined, meaning that the microprocessor-based clock used the highly accurate time signal received from WWV to trim the crystal oscillator. The timekeeping between updates was thus considerably more accurate than the crystal alone could have achieved. Time down to the tenth of a second was shown on an [[LED]] display. The GC-1000 originally sold for US$250 in kit form and US$400 preassembled, and was considered impressive at the time. Heath Company was granted a [http://patft.uspto.gov/netacgi/nph-Parser?Sect1=PTO1&Sect2=HITOFF&d=PALL&p=1&u=%2Fnetahtml%2FPTO%2Fsrchnum.htm&r=1&f=G&l=50&s1=4582434.PN.&OS=PN/4582434&RS=PN/4582434 patent] for its design.<ref>{{cite web |title=Heathkit GC-1000-H Most Accurate Clock |url=https://www.pestingers.net/pages-images/heathkit/radio-equipment/gc1000/gc1000.htm |website=Pestingers |archive-url=https://web.archive.org/web/20200214054036/https://www.pestingers.net/pages-images/heathkit/radio-equipment/gc1000/gc1000.htm |archive-date=February 14, 2020 |url-status=live}}</ref><ref>{{US patent reference |number = 4582434 |issue-date = April 15, 1986 |inventor = David Plangger and Wayne K. Wilson, Heath Company |title = Time corrected, continuously updated clock}}</ref>

By 1990, engineers from German watchmaker [[Junghans]] had miniaturized this technology to fit into the case of a digital wristwatch. The following year the analog version [[Junghans Mega|Junghans MEGA]] with hands was launched.

In the 2000s (decade) radio-based "atomic clocks" became common in retail stores; as of 2010 prices start at around US$15 in many countries.<ref>[http://www.kleenezeshop.com/products/2988-radio-controlled-clock.aspx/?affiliateid=779" Radio controlled clock £19.95] {{webarchive|url=https://archive.today/20130216084404/http://www.kleenezeshop.com/products/2988-radio-controlled-clock.aspx/?affiliateid=779 |date=2013-02-16}}</ref> Clocks may have other features such as indoor thermometers and [[weather station]] functionality. These use signals transmitted by the appropriate transmitter for the country in which they are to be used. Depending upon signal strength they may require placement in a location with a relatively unobstructed path to the transmitter and need fair to good atmospheric conditions to successfully update the time. Inexpensive clocks keep track of the time between updates, or in their absence, with a non-disciplined [[quartz-crystal clock]], with the accuracy typical of non-radio-controlled quartz timepieces. Some clocks include indicators to alert users to possible inaccuracy when synchronization has not been recently successful.

The United States [[National Institute of Standards and Technology]] (NIST) has published guidelines recommending that radio clock movements keep time between synchronizations to within ±0.5 seconds to keep time correct when rounded to the nearest second.<ref name="lombardi2" >[https://tf.nist.gov/general/pdf/2429.pdf "How Accurate is a Radio Controlled Clock?"] by Michael Lombardi (2010).</ref> Some of these movements can keep time between synchronizations to within ±0.2 seconds by synchronizing more than once spread over a day.<ref>[https://cdn.nedis.com/datasheets/MAN_HE-CLOCK-89_EN.PDF RADIO-CONTROLLED WALLCLOCK INSTRUCTION MANUAL]</ref>

Timepieces with [[Bluetooth]] radio support, ranging from watches with basic control of functionality via a [[mobile app]] to full [[smartwatch]]es<ref>{{cite web | title=Bluetooth| publisher=Casio| url=https://www.casio.com/europe/watches/technology/bluetooth/ | access-date=16 July 2024}}</ref> obtain time information from a connected [[Mobile phone|phone]], with no need to receive time signal broadcasts.