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A time signal is a visible, audible, mechanical, or electronic
signal A signal is both the process and the result of transmission of data over some media accomplished by embedding some variation. Signals are important in multiple subject fields including signal processing, information theory and biology. In ...
used as a reference to determine the time of day. Church bells or voices announcing hours of
prayer File:Prayers-collage.png, 300px, alt=Collage of various religionists praying – Clickable Image, Collage of various religionists praying ''(Clickable image – use cursor to identify.)'' rect 0 0 1000 1000 Shinto festivalgoer praying in front ...
gave way to automatically operated chimes on public
clock A clock or chronometer is a device that measures and displays time. The clock is one of the oldest Invention, human inventions, meeting the need to measure intervals of time shorter than the natural units such as the day, the lunar month, a ...
s; however, audible signals (even signal guns) have limited range. Busy seaports used a visual signal, the dropping of a ball, to allow mariners to check the chronometers used for navigation. The advent of electrical
telegraph Telegraphy is the long-distance transmission of messages where the sender uses symbolic codes, known to the recipient, rather than a physical exchange of an object bearing the message. Thus flag semaphore is a method of telegraphy, whereas ...
s allowed widespread and precise distribution of time signals from central observatories.
Railway Rail transport (also known as train transport) is a means of transport using wheeled vehicles running in railway track, tracks, which usually consist of two parallel steel railway track, rails. Rail transport is one of the two primary means of ...
s were among the first customers for time signals, which allowed synchronization of their operations over wide geographic areas. Dedicated radio time signal stations transmit a signal that allows automatic synchronization of clocks, and commercial broadcasters still include time signals in their programming. Today, global navigation satellite systems ( GNSS) radio signals are used to precisely distribute time signals over much of the world. There are many commercially available radio controlled clocks available to accurately indicate the local time, both for business and residential use. Computers often set their time from an Internet atomic clock source. Where this is not available, a locally connected GNSS receiver can precisely set the time using one of several software applications.


Audible and visible time signals

One sort of public time signal is a
striking clock A striking clock is a clock that sounds the hours audibly on a bell, gong, or other audible device. In 12-hour striking, used most commonly in striking clocks today, the clock strikes once at 1:00 am, twice at 2:00 am, continuing in this way up t ...
. These clocks are only as good as the clockwork that activates them, but they have improved substantially since the first clocks from the 14th century. Until modern times, a public clock such as Big Ben was the only time standard the general public needed. Accurate knowledge of time of day is essential for
navigation Navigation is a field of study that focuses on the process of monitoring and controlling the motion, movement of a craft or vehicle from one place to another.Bowditch, 2003:799. The field of navigation includes four general categories: land navig ...
, and ships carried the most accurate
marine chronometer A marine chronometer is a precision timepiece that is carried on a ship and employed in the determination of the ship's position by celestial navigation. It is used to determine longitude by comparing Greenwich Mean Time (GMT), and the time at t ...
s available, although they did not keep perfect time. A number of accurate audible or visible time signals were established in many
seaport A port is a maritime facility comprising one or more wharves or loading areas, where ships load and discharge cargo and passengers. Although usually situated on a sea coast or estuary, ports can also be found far inland, such as Hamburg, Manc ...
cities to enable navigators to set their chronometers.


Signal guns

In
Vancouver Vancouver is a major city in Western Canada, located in the Lower Mainland region of British Columbia. As the List of cities in British Columbia, most populous city in the province, the 2021 Canadian census recorded 662,248 people in the cit ...
,
British Columbia British Columbia is the westernmost Provinces and territories of Canada, province of Canada. Situated in the Pacific Northwest between the Pacific Ocean and the Rocky Mountains, the province has a diverse geography, with rugged landscapes that ...
, a " 9 O'Clock Gun" is still shot every night at 9 pm. (This gun was brought to
Stanley Park Stanley Park is a public park in British Columbia, Canada, that makes up the northwestern half of Vancouver's Downtown Vancouver, Downtown peninsula, surrounded by waters of Burrard Inlet and English Bay, Vancouver, English Bay. The park bor ...
in 1894 by the Department of Fisheries originally to warn fishermen of the 6:00 pm Sunday closing of fishing.) The 9:00 pm firing was later established as a time signal for the general population. Until a time gun was installed, the nearby Brockton Point lighthouse keeper detonated a stick of dynamite. Elsewhere in Canada, a "Noon Gun" is fired daily from the citadels in Halifax and
Quebec City Quebec City is the capital city of the Provinces and territories of Canada, Canadian province of Quebec. As of July 2021, the city had a population of 549,459, and the Census Metropolitan Area (including surrounding communities) had a populati ...
and from Signal Hill in St. John's, Newfoundland and Labrador. In the same manner, a Noon Gun has been fired in
Cape Town Cape Town is the legislature, legislative capital city, capital of South Africa. It is the country's oldest city and the seat of the Parliament of South Africa. Cape Town is the country's List of municipalities in South Africa, second-largest ...
, since 1806. The gun is fired daily from the Lion Battery at Signal Hill. The Noonday Gun serves a similar purpose in
Hong Kong Hong Kong)., Legally Hong Kong, China in international treaties and organizations. is a special administrative region of China. With 7.5 million residents in a territory, Hong Kong is the fourth most densely populated region in the wor ...
. The tradition, which started in the 1860s under British colonial rule, has become a tourist attraction in recent times. A cannon was fired at one o'clock every weekday at
Liverpool Liverpool is a port City status in the United Kingdom, city and metropolitan borough in Merseyside, England. It is situated on the eastern side of the River Mersey, Mersey Estuary, near the Irish Sea, north-west of London. With a population ...
, at the
Castle A castle is a type of fortification, fortified structure built during the Middle Ages predominantly by the nobility or royalty and by Military order (monastic society), military orders. Scholars usually consider a ''castle'' to be the private ...
in
Edinburgh Edinburgh is the capital city of Scotland and one of its 32 Council areas of Scotland, council areas. The city is located in southeast Scotland and is bounded to the north by the Firth of Forth and to the south by the Pentland Hills. Edinburgh ...
, and also at
Perth Perth () is the list of Australian capital cities, capital city of Western Australia. It is the list of cities in Australia by population, fourth-most-populous city in Australia, with a population of over 2.3 million within Greater Perth . The ...
to establish the time. The Edinburgh " One O'Clock Gun" is still in operation. A cannon located at the top of Santa Lucia Hill, in
Santiago Santiago (, ; ), also known as Santiago de Chile (), is the capital and largest city of Chile and one of the largest cities in the Americas. It is located in the country's central valley and is the center of the Santiago Metropolitan Regi ...
, is shot every noon. In
Rome Rome (Italian language, Italian and , ) is the capital city and most populated (municipality) of Italy. It is also the administrative centre of the Lazio Regions of Italy, region and of the Metropolitan City of Rome. A special named with 2, ...
, on the Janiculum, a hill west of the
Tiber The Tiber ( ; ; ) is the List of rivers of Italy, third-longest river in Italy and the longest in Central Italy, rising in the Apennine Mountains in Emilia-Romagna and flowing through Tuscany, Umbria, and Lazio, where it is joined by the R ...
since 1904 a cannon is fired daily at noon towards the river as a time signal. This was introduced in 1847 by
Pope Pius IX Pope Pius IX (; born Giovanni Maria Battista Pietro Pellegrino Isidoro Mastai-Ferretti; 13 May 1792 – 7 February 1878) was head of the Catholic Church from 1846 to 1878. His reign of nearly 32 years is the longest verified of any pope in hist ...
to synchronise all the church bells of Rome. It was situated in Castel Sant'Angelo until 1903 when it was moved to
Monte Mario Monte Mario (English: Mount Mario or Mount Marius) is the hill that rises in the north-west area of Rome (Italy), on the right bank of the Tiber, crossed by the Via Trionfale. It occupies part of Balduina, of the territory of Municipio I, Munici ...
for a few months until it was placed in its current position. The cannon was silenced from the start of
WWII World War II or the Second World War (1 September 1939 – 2 September 1945) was a World war, global conflict between two coalitions: the Allies of World War II, Allies and the Axis powers. World War II by country, Nearly all of the wo ...
for about twenty years until 21 April 1959, the 2712th anniversary of Rome's founding, and has been in use since then. For many years an old cannon was fired "about noon" from a mountain near
Kabul Kabul is the capital and largest city of Afghanistan. Located in the eastern half of the country, it is also a municipality, forming part of the Kabul Province. The city is divided for administration into #Districts, 22 municipal districts. A ...
.


Sirens, whistles, and other audible signals

In many Midwestern US cities where tornadoes are a common hazard, the emergency sirens are tested regularly at a specified time (say, noon each Saturday); while not primarily intended to mark the time, local people often check their watches when they hear this signal. In many non-seafaring communities, loud factory whistles served as public time signals before radio made them obsolete. Sometimes, the tradition of a factory whistle becomes so deeply entrenched in a community that the whistle is maintained long after its original function as a time keeper became obsolete. For example, the
University of Iowa The University of Iowa (U of I, UIowa, or Iowa) is a public university, public research university in Iowa City, Iowa, United States. Founded in 1847, it is the oldest and largest university in the state. The University of Iowa is organized int ...
's power plant whistle has been reinstated several times by popular demand after numerous attempts to silence it.


Visual signals

In 1861 and 1862, the Edinburgh Post Office Directory published time gun maps relating the number of seconds required for the report of the time gun to reach various locations in the city. Because
light Light, visible light, or visible radiation is electromagnetic radiation that can be visual perception, perceived by the human eye. Visible light spans the visible spectrum and is usually defined as having wavelengths in the range of 400– ...
travels much faster than
sound In physics, sound is a vibration that propagates as an acoustic wave through a transmission medium such as a gas, liquid or solid. In human physiology and psychology, sound is the ''reception'' of such waves and their ''perception'' by the br ...
, visible signals enabled greater precision than audible ones, although audible signals could operate better under conditions of reduced visibility. The first time ball was erected at
Portsmouth Portsmouth ( ) is a port city status in the United Kingdom, city and unitary authority in Hampshire, England. Most of Portsmouth is located on Portsea Island, off the south coast of England in the Solent, making Portsmouth the only city in En ...
, England in 1829 by its inventor Robert Wauchope.Aubin, Davi
The Heavens on Earth: Observatories and Astronomy in Nineteenth-Century Science and Culture
p.164. Duke University Press, 2010
One was installed in 1833 on the roof of the Royal Observatory in
Greenwich Greenwich ( , , ) is an List of areas of London, area in south-east London, England, within the Ceremonial counties of England, ceremonial county of Greater London, east-south-east of Charing Cross. Greenwich is notable for its maritime hi ...
, London, and the time ball has dropped at 1:00 pm every day since then. The first American time ball went into service in 1845. In New York City, the ceremonial Times Square Ball drop on New Year's Eve in
Times Square Times Square is a major commercial intersection, tourist destination, entertainment hub, and Neighborhoods in New York City, neighborhood in the Midtown Manhattan section of New York City. It is formed by the junction of Broadway (Manhattan), ...
is a vestige of a visual time signal.


Electrical time signals


United Kingdom

The first telegraph distribution of time signal in the United Kingdom, indeed, in the world, was initiated in 1852 by the Electric Telegraph Company in collaboration with the
Astronomer Royal Astronomer Royal is a senior post in the Royal Households of the United Kingdom. There are two officers, the senior being the astronomer royal dating from 22 June 1675; the junior is the astronomer royal for Scotland dating from 1834. The Astro ...
.
Greenwich Mean Time Greenwich Mean Time (GMT) is the local mean time at the Royal Observatory, Greenwich, Royal Observatory in Greenwich, London, counted from midnight. At different times in the past, it has been calculated in different ways, including being ...
was distributed by telegraph from the Greenwich Observatory. This included a system for synchronising the drop of the time ball at Greenwich with other time balls around the country, one of which was atop the Electric's offices in the Strand. Other synchronised time balls were atop the Nelson Monument, Edinburgh; the sailors' home Broomielaw, Glasgow;
Liverpool Liverpool is a port City status in the United Kingdom, city and metropolitan borough in Merseyside, England. It is situated on the eastern side of the River Mersey, Mersey Estuary, near the Irish Sea, north-west of London. With a population ...
and one at Deal, Kent, installed by the Admiralty.Kieve, Jeffrey L., ''The Electric Telegraph: A Social and Economic History'', pp. 52-53, David and Charles, 1973 .


United States

Telegraph signals were used regularly for time coordination by the United States Naval Observatory starting in 1865. By the late 1800s, many U.S. observatories were selling accurate time by offering a regional time signal service.
Sandford Fleming Sir Sandford Fleming (January 7, 1827 – July 22, 1915) was a Scottish Canadian engineer and inventor. Born and raised in Scotland, he immigrated to colonial Canada at the age of 18. He promoted worldwide standard time zones, a prime meridian, ...
proposed a single 24-hour clock for the entire world. At a meeting of the Royal Canadian Institute on 8 February 1879 he linked it to the anti-meridian of Greenwich (now 180°). He suggested that standard
time zone A time zone is an area which observes a uniform standard time for legal, Commerce, commercial and social purposes. Time zones tend to follow the boundaries between Country, countries and their Administrative division, subdivisions instead of ...
s could be used locally, but they were subordinate to his single world time.
Standard time Standard time is the synchronization of clocks within a geographical region to a single time standard, rather than a local mean time standard. Generally, standard time agrees with the local mean time at some meridian that passes through the r ...
came into existence in the United States on 18 November 1883. Earlier, on 11 October 1883, the General Time Convention, forerunner to the American Railway Association, approved a plan that divided the United States into several
time zone A time zone is an area which observes a uniform standard time for legal, Commerce, commercial and social purposes. Time zones tend to follow the boundaries between Country, countries and their Administrative division, subdivisions instead of ...
s. On that November day, the US Naval Observatory telegraphed a signal that coordinated noon at Eastern standard time with 11 am Central, 10 am Mountain, and 9 am Pacific standard time. A March 1905 issue of ''The Technical World'' describes the role of the United States Naval Observatory as a source of time signals: :''One of the most important functions of the Naval Observatory is found in the daily distribution of the correct time to every portion of the United States. This is effected by means of telegraphic signals, which are sent out from Washington at noon daily, except Sundays. The original object of this time service was to furnish mariners in the seaboard cities with the means of regulating their chronometers; but, like many another governmental activity, its scope has gradually broadened until it has become of general usefulness. The electrical impulse which goes forth from the Observatory at noon each day, now sets or regulates automatically more than 70,000 clocks located in all parts of the United States, and also serves, in each of the larger cities of the country, to release a time-ball located on some lofty building of central location. The dropping of the time-ball – accompanied, at some points, with the simultaneous firing of a cannon – is the signal for the regulation by hand of hundreds of other clocks and watches in the vicinity.''


Radio time sources


Dedicated time signal broadcasts

The telegraphic distribution of time signals was made obsolete by the use of AM, FM,
shortwave radio Shortwave radio is radio transmission using radio frequencies in the shortwave bands (SW). There is no official definition of the band range, but it always includes all of the High frequency, high frequency band (HF), which extends from 3 to 30& ...
, Internet
Network Time Protocol The Network Time Protocol (NTP) is a networking protocol for clock synchronization between computer systems over packet-switched, variable-Network latency, latency data networks. In operation since before 1985, NTP is one of the oldest Intern ...
servers as well as
atomic clock An atomic clock is a clock that measures time by monitoring the resonant frequency of atoms. It is based on atoms having different energy levels. Electron states in an atom are associated with different energy levels, and in transitions betwee ...
s in
satellite navigation A satellite navigation or satnav system is a system that uses satellites to provide autonomous geopositioning. A satellite navigation system with global coverage is termed global navigation satellite system (GNSS). , four global systems are ope ...
systems. Time signals have been transmitted by radio since 1905. There are dedicated radio time signal stations around the world. Time stations operating in the
longwave In radio, longwave (also spelled long wave or long-wave and commonly abbreviated LW) is the part of the radio spectrum with wavelengths longer than what was originally called the medium-wave (MW) broadcasting band. The term is historic, dati ...
radio band have highly predictable
radio propagation Radio propagation is the behavior of radio waves as they travel, or are wave propagation, propagated, from one point to another in vacuum, or into various parts of the atmosphere. As a form of electromagnetic radiation, like light waves, radio w ...
characteristics, which gives low uncertainty in the received time signals. Stations operating in the shortwave band can cover wider areas with relatively low-power transmitters, but the varying distance that the signal travels increases the uncertainty of the time signal on a scale of milliseconds. Radio time signal stations broadcast the time in both audible and machine-readable time code form that can be used as references for
radio clock A radio clock or radio-controlled clock (RCC), and often colloquially (and incorrectly) referred to as an "atomic clock", is a type of Quartz clock, quartz clock or watch that is automatically Synchronization, synchronized to a time code transmi ...
s and radio-controlled watches. Typically, they use a national or regional
longwave In radio, longwave (also spelled long wave or long-wave and commonly abbreviated LW) is the part of the radio spectrum with wavelengths longer than what was originally called the medium-wave (MW) broadcasting band. The term is historic, dati ...
digital signal; for example, station WWVB in the U.S. . The audio portions of the shortwave WWV and WWVH broadcasts can also be heard by telephone. The time announcements are normally delayed by less than 30 ms when using land lines from within the continental United States, and the stability (delay variation) is generally However, when mobile phones are used, the delays are often more than 100 ms, due to the multiple access methods used to share cell channels. In rare instances when the telephone connection is made by satellite, the time is delayed by 250–500 ms. The audio from the broadcasts is available by telephone by dialling U.S. numbers for WWV (Colorado), and for WWVH (Hawaii). Calls (which are ''not'' toll-free) are disconnected after 2 minutes. Loran-C time signals formerly were also used for radio clock synchronization, by augmenting their highly accurate frequency transmissions with external measurements of the offsets of LORAN navigation signals against time standards.


General broadcasters

As radio receivers became more widely available, broadcasters included time information in the form of voice announcements or automated tones to accurately indicate the hour. The
BBC The British Broadcasting Corporation (BBC) is a British public service broadcaster headquartered at Broadcasting House in London, England. Originally established in 1922 as the British Broadcasting Company, it evolved into its current sta ...
has included time " pips" in its broadcasts from 1922. In the United States many information-based radio stations (full-service, all-news and news/talk) also broadcast time signals at the beginning of the hour. In New York, WCBS and WINS have distinctive beginning-of-the-hour tones, though the WINS signal is only approximate (several seconds error). WINS also has a tone at 30 minutes past the hour for those setting their clocks. WTIC uses the
Morse code Morse code is a telecommunications method which Character encoding, encodes Written language, text characters as standardized sequences of two different signal durations, called ''dots'' and ''dashes'', or ''dits'' and ''dahs''. Morse code i ...
 V for victory to the tune of Beethoven's 5th Symphony at the beginning of the hour continuously, since 1943. Broadcast stations using iBiquity Digital's "
HD Radio HD Radio (HDR) is a trademark for in-band on-channel (IBOC) digital radio broadcast technology. HD radio generally simulcast, simulcasts an existing analog radio station in digital format with less noise and with additional text information. HD R ...
" system are contractually required to delay their analog broadcast by about eight seconds, so it remains in sync with the digital stream. Thus, network-generated time signals and service cues will also be delayed by about eight seconds. (Because of the delay, when WBEN-AM in
Buffalo, New York Buffalo is a Administrative divisions of New York (state), city in the U.S. state of New York (state), New York and county seat of Erie County, New York, Erie County. It lies in Western New York at the eastern end of Lake Erie, at the head of ...
was broadcasting time markers, and was simulcast on an FM station that broadcast in HD; the FM signal did not carry the time signal. WBEN does not broadcast in HD.) Local signals may also be delayed. The
all-news radio All-news radio is a radio format devoted entirely to the discussion and broadcast of news. All-news radio is available in both local and radio syndication, syndicated forms, and is carried on both major US satellite radio networks. All-news sta ...
stations of the CBS Radio Network, of which WCBS is the flagship, air a "bong" (at a frequency of 440 Hz – the international standard for the musical note ) that immediately precedes each top-of-the-hour network newscast. (The same bong could be heard on the CBS Television Network, at the top of the hour immediately before the beginning of any televised program, in the 1960s and 1970s.) An automated "chirp" at one second before the hour signals a switch to the radio network broadcast. As an example, KNX, the CBS Radio Network all-news station in Los Angeles, broadcasts this "bong" sound on the hour. However, due to buffering of the digital broadcast on some computers, this signal may be delayed as much as 20 seconds from the actual start of the hour (this is presumably the same situation for all CBS Radio stations, as each station's digital stream is produced and distributed in a similar manner), though unlike program content which is on a
broadcast delay In radio and television, broadcast delay is an intentional delay when broadcasting live material, technically referred to as a deferred live. Such a delay may be to prevent mistakes or unacceptable content from being broadcast. Longer delays las ...
for content concerns, the time signal airs as-is over-the-air, meaning it can sometimes be talked over during a live news event or sports play-by-play. KYW-AM in Philadelphia broadcasts a time signal at the top of the hour along with its
jingle A jingle is a short song or tune used in advertising and for other commercial uses. Jingles are a form of sound branding. A jingle contains one or more hooks and meanings that explicitly promote the product or service being advertised, usually ...
. Bonneville International-owned news/talk station KSL (AM-FM) in Salt Lake City uses a "clang" that originates from the Nauvoo Bell on Temple Square, in Salt Lake City, which has been a staple on the station since the early 1960s. In Canada, the national English-language non-commercial
CBC Radio One CBC Radio One is the English-language news and information radio network of the publicly owned Canadian Broadcasting Corporation. It is commercial-free and offers local and national programming. It is available on AM and FM to 98 percent o ...
network broadcast the daily National Research Council Time Signal from 5 November 1939 until 9 October 2023. The simulcast would occur daily at 1pm
Eastern Time The Eastern Time Zone (ET) is a time zone encompassing part or all of 23 states in the eastern part of the United States, parts of eastern Canada, and the state of Quintana Roo in Mexico. * Eastern Standard Time (EST) is five hours behi ...
. Its French-language counterpart, Radio-Canada, broadcasts a similar signal at noon.
Vancouver Vancouver is a major city in Western Canada, located in the Lower Mainland region of British Columbia. As the List of cities in British Columbia, most populous city in the province, the 2021 Canadian census recorded 662,248 people in the cit ...
radio station CKNW also broadcasts time signals, using a chime every half-hour. Time signals on CBC broadcasts may be delayed up to 3 seconds due to network processing delays between the local radio transmitter and the time signal origin in Ottawa. The CBC's predecessor, the Canadian National Railways Radio network, broadcast the time signal over its Ottawa station, CNRO (originally CKCH), at 9 pm daily and also on its Moncton station, CNRA, beginning in 1923. CNRA closed in 1931 but the broadcasts continued on CNRO when the station was acquired by the Canadian Radio Broadcasting Commission in 1933 and by the CBC in 1936 before going national in 1939. In Australia, many information-based radio stations broadcast time signals at the beginning of the hour, and a speaking clock service was also available until October 2019. However, the VNG dedicated time signal service has been discontinued. In Cuba, Radio Reloj is a radio station which has a time signal over news. Radio Reloj translates to Clock Radio.


Digital delay

Program material, including time signals, that is transmitted digitally (e.g. DAB,
Internet radio Internet radio, also known as online radio, web radio, net radio, streaming radio, e-radio and IP radio, is a digital audio service transmitted via the Internet. Broadcasting on the Internet is usually referred to as webcasting since it is not ...
) can be delayed by tens of seconds due to buffering and error correction, making time signals received on a digital radio unreliable when accuracy is needed.


See also

* Car radio,
Radio Data System Radio Data System (RDS) is a communications protocol standard for embedding small amounts of digital information in conventional FM broadcasting, FM radio broadcasts. RDS standardizes several types of information transmitted, including time, sta ...
(RDS) * Clock signal * Extended Data Services and PBS * * Greenwich Time Signal * Low frequency, (LF) * Smart Personal Objects Technology, (SPOT) * Speaking clock *
Synchronization Synchronization is the coordination of events to operate a system in unison. For example, the Conductor (music), conductor of an orchestra keeps the orchestra synchronized or ''in time''. Systems that operate with all parts in synchrony are sa ...
* VBI, VITC * WWVB * Time synchronization in North America * Time transfer * Time and frequency transfer * Time synchronization


References


Further reading

*


External links

* * — mentions the time cannon at
Perth Perth () is the list of Australian capital cities, capital city of Western Australia. It is the list of cities in Australia by population, fourth-most-populous city in Australia, with a population of over 2.3 million within Greater Perth . The ...
* — mentions the time cannon at
Cape Town Cape Town is the legislature, legislative capital city, capital of South Africa. It is the country's oldest city and the seat of the Parliament of South Africa. Cape Town is the country's List of municipalities in South Africa, second-largest ...
* — The VNG Users' Consortium was working on ways to solve the problem of the lack of accurate time signals in Australia. * * : :: ''Magazine was published from 1904–1905 by the Armour Institute of Technology.'' * * {{Time measurement and standards Horology