We know the language of clocks and timekeeping solutions can sometimes be a bit confusing. Please reference this Glossary of Terms if you need clarification, or call the Clock Experts at 800-328-8996 for more information.


2 Wire Synchronous – See Electronic Synchronous System Clock.

3 Wire Synchronous – Power is continuously furnished to the clock run motor. Correction signal comes in on a separate line to furnish power to the clock correction coil.

12-Hour Correction – The signal from the master clock which is sent every 12 hours to correct the hour hand. It is longer in duration than the hourly correction, and usually occurs between the hours of 5:00 and 6:00, both a.m. and p.m..


Atomic Clock – A clock with an internal atomic oscillator. Radio controlled clocks are often referred to as atomic clocks, which is a misnomer. See Radio Controlled Clocks.

Auto-Correct After Power Failure – A clock connected to a master clock with a battery back-up will adjust to the correct time after receiving a 12-hour correction.

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Backbox – Metal enclosure usually recessed into the wall that houses the movement of a flush mount wall clock.

Back Plate – The plate the movement is mounted to.

Battery Clock – A clock powered by a battery.

Bezel – The main housing or frame of the clock. Typically, it is round or square and is made of wood, metal or plastic. Also referred to as the clock case.

Booster – A unit designed to increase the power going through the wires to the clock.

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Clock Case – See Bezel.

Chapter – A term referring to different designs for dial numbering (dial style).

Clock School – A free training seminar on how your master clock controller and system clocks operate. It is offered at the American Time factory or can be conducted on-site at your request.

CMB – Center mount bushing.

Correction Coil – The magnetic electrical device activated by the correction line signal that causes the movement to go into correction mode for each minute, hour or every 12 hours.

Convex – Curving outward from the clock dial.

Coordinated Universal Time (UTC) – The 24-hour based international atomic time scale. It is the time of day at the Earth’s prime meridian (0 deg. Longitude). Sometimes still referred to as Greenwich Mean Time, which is a misnomer. Local UTC is determined by either adding or subtracting hours to or from UTC depending on the longitude of your location.

Correction  The process of syncing clocks that are off-time at initial start-up or after power outages.

Crystal – The lens of the clock used to protect the dial and hands, usually made of glass or plastic.

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Dial – The visible face of the clock with marked graduations for reference to the hands for measuring the progression of time. Also referred to as the clock face.

Digital Clock – A clock that displays time with numerical display (12:00). 

Double Dial – A mounting bracket that has a clock face on both sides, typically wall or ceiling mounted in hallways so time can be viewed from both directions.

Dust Cover – A cover over the clock movement to protect it from excessive dust build-up.

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Electrical Box – Metal or plastic enclosure usually sunk into a wall that houses electrical wires.

Electric Clock – A clock typically powered (wired) by an 120vac or 24vac source. A battery back-up might be available for power outages.

Electronic Synchronous System Clock – A clock that synchronizes off a specific frequency and duration generated and added to the electrical carrier lines throughout a building. This “signal” acts as the trigger mechanism to put the clocks into correction and allows them to be plugged into any electrical outlet within a facility to receive correction signal.

Ethernet – A popular technology for networking computers and other devices. This communication method can be used for transmitting and receiving precise timing signals by the SiteSync IQ System Controller, the AllSync IQ Master Clock and Power over Ethernet (PoE) clocks.

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Flush Mount – A clock with the movement mounted inside a backbox to give the clock a low profile against the wall.

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Gauge – Measurement of size for wire or metal.  Ex: 3 gauge wire or 20 gauge steel.

GPS – Global Positioning System. A constellation of satellites operated by the United States Military (U.S. Naval Observatory) that broadcasts precisely timed signals from space. The signals are used for extremely accurate global navigation, as well as the distribution of precise time.

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Hourly Correction – The signal from the master clock sent every hour to correct the minute hand and, where applicable, the sweep second hand.

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Impulse – Secondary clock that receives a DC pulse every minute from a master clock to stay on time. Impulse clocks do not have a sweep second hand.

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Lens – See Crystal.

LED – Light Emitting Diode. Used to light numbers on digital boards or illuminate backlit clocks.

LCD – Liquid Crystal Display. A flat panel used in watches and some clocks to display visible characters.

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Master Clock – In a timekeeping or clock system, a device that acts as the source of time. The Master Clock, or System Controller, transmits the time to any number of secondary clocks.

Motor – Runs the clock movement, usually 120v or 24v.

Movement (motor movement) – A mechanism, consisting of a clock motor and gear box. May also have a correction coil.

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NEMA – National Electrical Manufacturers Association. An organization providing a forum for the standardization of electrical equipment, enabling consumers to select from a range of safe, effective and compatible electrical products.

NIST – National Institute of Standards and Technology. The Time and Frequency Division, part of NIST’s Physics Laboratory, maintains the standard for frequency and time interval for the United States and provides official time to the United States. This includes traceability from the GPS timing signals to the NIST national frequency standard.

Non-Corrective – Clock that does not receive a correction signal for synchronization and powered by 120v, 24v or battery source.

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Personalization – Clock dials from American Time  can be customized with graphics or text to meet you or your customer’s, needs. Logos, mascots and names are most common.

Power over Ethernet (PoE) – Power over Ethernet clocks, also known as IP network clocks, Ethernet clocks and NTP clocks, deliver both power and time updates through one cable connected to a facility’s Ethernet.

Power Supply – Unit designed to supply power through wires to power the clock.

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Quartz Movement – A movement that utilizes a battery for its power source.

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Radio Controlled Clock – A clock that receives a NIST radio signal and uses the signal to automatically synchronize time to the atomic clock in Ft. Collins, Colo.

Reset Stem or Shaft – Used on a clock to manually change the time.

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Schedule – A group of events. For example, a school might program Schedule 01 with four events for their morning Elementary recess schedule.

Synchronization – The process of bringing two clocks or time sources into phase so their difference is zero. In timekeeping systems, time synchronization takes place between the master clock and all secondary clocks.

Secondary Clock – A clock that is synchronized by a signal from a system master clock.

Stand-Alone Clock – See Non-Corrective.

Surface Mount – A clock with a movement that does not protrude past the bezel, or clock case, and mounts flat against the wall without a backbox, giving it a deeper profile.

Sweep Second Hand – The hand of the clock that indicates or measures seconds of time.

Synchronous – Power is continuously furnished to the clock drive motor.

System Clock – A clock that receives its power from a master clock for both run and correction, and is directly wired to the master clock.

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UL – Underwriters Laboratories, Inc. A testing organization that develops standards and test procedures for components and equipment, typically dealing with product safety.

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Vinyl-Clad – Metal that has a vinyl coating applied to one or both sides.

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Weatherproof – Ability to withstand harsh weather conditions or exposure to precipitation.

Weather-resistant – Ability to offer resistance to bad weather or exposure to precipitation.

Wi-Fi Clocks – Receive the time signal from an existing Wi-Fi infrastructure. No master clock is needed for correction. 

Wired Synchronous – A clock connected to a master clock by three wires for both run and correction.

Wireless Clock System – A system controller, sometimes called a master clock, that pulls time from an Ethernet cable, GPS satellite or cell phone tower. The system controller transmits its own wireless signal directly to each of the wireless clocks.

WWVB – A NIST Radio Station located near Ft. Collins, Colo., that broadcasts time and frequency signals at 60 KHz. The broadcast is picked up by radio controlled clocks, allowing the clock’s movement to synchronize with the broadcasted time.

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