Clocks and Timers

This section includes a wide selection of devices designed to make linear and absolute measurements of time. Such devices include clocks, interval timers, time locks, time switches and digital counters. A wide range of technologies are utilized in industrial timepieces, ranging from conventional spring-driven mechanical movements to synchronous motors and exotic electromechanical mechanisms.

 


Elgin Gun Camera Clock
 

This diminutive mechanical clock is designed for a very unusual role, recording timestamps in a film based "gun camera" mounted to the side of a military aircraft. Gun cameras were used on military aircraft to record damage to enemy targets, and military intelligence specialists found it useful to have a timestamp attached to each photo. To provide this, a small clock would be mounted inside the camera; a series of prisms would superimpose the clock face in a corner of the camera's field of view, which would then be recorded every time the camera took a picture. This clock makes use of an Elgin 685 movement, a movement type that is typically used for 24 hour wristwatches. Some gun camera clocks are electrically wound, but this clock has an external crown for winding and setting similar to the type found on a wristwatch. In operation the clock would be mounted in a removable compartment on the camera and would need to be wound and set before the start of a mission.

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Elgin Gun Camera Clock
Eaton Two Movement Time Lock
 

A time lock is a special type of clock designed to be mounted inside of a bank vault or high-security safe. Time locks are designed to prevent robberies by sealing a bank vault until a designated amount of time passes, which prevents a potential robber from kidnapping the bank manager after hours and forcing him or her to open the vault door. This time lock mechanism, manufactured by Eaton, is a typical example of the style of time lock used during the Cold War. The lock contains two complete and separate spring-driven clock movements for redundancy, either movement can trigger the lock's release mechanism. Each movement has a dial with a small pin attached that indicates the amount of time remaining before the vault can be opened; the pins engage levers along the bottom of the movement that free the bolt on the vault door when the dials are at the zero position. Note that in the thumbnail the cover and bolt-work for the lock have been removed to allow the movements to be seen. The dials are set and the movements wound with a key that inserted through a pair of small holes on the face of the lock.

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Eaton Two Movement Time Lock
B52 MD-1 Astro Navigation Aircraft Clock
 

This unusual device is the clock out of a MD-1 Astro Navigation system, which was the navigation system used on B-52 bombers prior to the invention of inertial guidance systems. Sometimes called the Star Tracker system, this complicated device made use of an electromechanical sextant mounted to the top of the aircraft, linked to an array of controls and computer modules. When in operation the Astro Navigation system would track the positions of up to three stars (or the Sun), and calculate the aircraft's current position. This clock is powered by a 28 volt, 400hz synchronous motor which also serves as the device's timebase. The clock contains no external setting controls, but a complicated system of synchro transmitters and synchronous motors allow the clock to be set and read by the star tracker system. In normal operation this clock would have been sealed in an airtight gas filled enclosure, and a valve stem has been attached to the back panel of the clock to allow filling and removal of gas after the case is sealed.

When first released, the clock in the MD-1 Astro Navigation system was notoriously inaccurate. This was solved in later versions by the addition of a new tuning fork timebase, which supplied a clean 400Hz signal to the clock's synchronous motor.

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B52 MD-1 Astro Navigation Aircraft Clock
General Electric 3T18SOL2 Astronomic Time Switch
 

Back in the hallowed days of our transistor-anemic past, turning light bulbs on and off at preset times was a seriously complicated task - so much so that when the City of New York was hard-up for a way to control its streetlights automatically, they made the dubious decision to mount metal-clad Telechron clocks to every street corner. These devices, manufactured by General Electric, were encased in a heavy vandal-resistant cast case and have a complex internal mechanism that implements a 365 day calendar and automatic daylight compensation. The metal pins that operate the time switch are mounted to a pair of rotating levers that move independently of the main dial. These levers are positioned by a 364 tooth calendar gear that completes one rotation relative to the main dial every year, allowing the switch to automatically match the operating time of the streetlamp to the length of the day.

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General Electric 3T18SOL2 Astronomic Time Switch
Sargent & Greenleaf Type L Time Lock Movement
 

Sargent & Greenleaf is a prolific manufacturer of time locks and time lock components, and the Type L movement is a typical example of the type of movements used in older Sargent & Greenleaf time locks. Unlike most manufacturers of this era, which used movements manufactured by the E. Howard watch company, Sargent & Greenleaf constructed their own movements in-house. As a result, Sargent & Greenleaf time lock movements contain many distinctive design choices, such as a characteristic 'wagon wheel'-style dial and an unusual jeweled escapement that does not include a roller gem on the balance wheel. These movements were designed to be used in groups for redundancy; typically two or three movements would be installed in a single time lock. We have been unable to accurately date this item, but suspect it was manufactured sometime between 1890 and 1920.

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Sargent & Greenleaf Type L Time Lock Movement
Longines Wittnauer A7 Aircraft Clock
 

World War 2 and the buildup immediately preceeding it saw the manufacture of numerous different types of aircraft clocks, and this Longines Wittnauer A7 clock is one such example. A7 model clocks differ from the much more common A6 model in that they have a 'pendant wind' winding stem which exits the bottom of the case instead of extending vertically below the 6-o-clock position. A metal plug has been pressed into the winding stem hole that would have been used in an A6 model clock. This clock makes use of a Jaeger LeCoultre 201M caliber movement, a relatively high end time-only movement with a 7 jewel lever escapement. This model of clock was also manufactured with a less common and more expensive 14 jewel movement.

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Longines Wittnauer A7 Aircraft Clock
Ohmer Fare Register
 

Back in the time before Uber and digital electronics, taxi drivers would make use of elaborate mechanical taximeters. These devices, which were typically mounted between the driver and passenger seat of a taxi, contained a complex mechanical integrator which would combine time and distance traveled to calculate the fare a customer would pay for a trip. The example shown here, manufactured in the mid 1930s by the Ohmer Fare Register company of Dayton Ohio, has had it's cover removed so the internal mechanism can be seen. The bottom half of the machine contains a brass clock movement and a connection that linked to the taxi's odometer by means of a flexible cable. The integrated outputs from these two systems would advance a large mechanical counter on the front of the device; this would face the passenger when installed between the seats of a taxi.

The inside of this fare register is a dense forest of cogs and stamped steel levers worthy of a tired Rube Goldberg comparison. The only electrical component in the entire mechanism is a single leaf switch on the side of the device. This switch closes when the driver turns off the taximeter, and would connect to a lamp on the roof of the taxi to indicate that it is 'available' to potential customers. While much less convenient than a smartphone app, such a system does have the benefit of being completely free of pop-up ads and viral internet cat videos.

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Ohmer Fare Register Taximeter
Sangamo KA-21 & WA-21 Synchronous Time Switches
 

Before the global microprocessor invasion, Sangamo synchronous time switches were the definitive method for controlling exterior lamps and other electrical devices that would need to be powered on and off in accordance with a pre-determined schedule. Sangamo time switches contain a large electromechanical clock movement that drives a rotating metal disk. The disk has a number of movable 'fingers', which varies from model to model: the KA-21 is equipped with six, while the WA-21 has only four. The schedule is set by moving the fingers around the disk to the appropriate time. As the disk makes a revolution, the fingers push mechanical levers which open and close a set of electrical contacts.

Both the KA-21 and WA-21 have a rectangular glass window on their face to verify the set schedule, as well as a smaller, circular window for observing the synchronous motor in operation.

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Sangamo KA-21 & WA-21 Synchronous Time Switches
Telechron Occlusion Clock
 

This bizarre and hard-to-find device is a purely mechanical illuminated display, which utilizes a series of slides to block light and display numbers. Each digit consists of an X and Y axis slide: the X axis slide contains all of the segment patterns needed to display numbers using the four vertical segments, and the Y axis slide contains all of the patterns needed to display numbers with the three horizontal segments. A series of cams move the slides in lock-step, opening and closing the slots in the front of the device as needed to display numbers. This display is a fully contained clock module, and includes a synchronous motor and alarm mechanism that closes a set of contacts when the alarm is tripped. Four knobs below the display allow setting of the time and alarm, as well as activation and deactivation of the alarm and manual closure of the alarm contacts.

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Telechron Occlusion Clock
Wakmann A-11 Aircraft Clock
 

The A-11 is one of the most common styles of aircraft clock in the world, and the clock pictured here, manufactured by Wakmann, is a fairly representative example. A-11 form factor clocks are basic, time only devices with three hands and a winding and setting stem located in the lower corner of the face. A threaded plug on the back of the case can be removed to gain access to the regulator lever without dismantling the entire clock. Most have a standard 12 hour dial, though 24 hour dials, such as shown here, are also sometimes used. This clock contains a 7 jewel movement manufactured by Revue Thommen, a newer movement that saw use in many different models of aircraft clocks. The example shown here was manufactured in October of 1977.

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Wakmann A-11 Aircraft Clock

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