The Complete Guide to Vintage Station and Factory Clocks
INTRODUCTION
Look up in an old railway station, a school corridor or a factory hall and you will often find the same thing: a large, plain clock with bold numerals. What most people never realise is that this clock could not tell the time on its own. It was a slave clock, one voice in a choir conducted by a single master clock hidden somewhere in the building.
In this guide we explain how these systems worked, who built them, and what to look for when you bring one into your own interior. Every clock in our collection once belonged to such a network.
ONE TIME FOR EVERYONE: WHY MASTER CLOCK SYSTEMS EXISTED
EVERY TOWN ITS OWN TIME
Before the railways, every town kept its own local time. That worked until trains began running to timetables. In the 1840s British railways started running on London time, and the need for one shared, exact time spread quickly to stations, post offices, factories and schools.
ONE CLOCK IS EASY, A HUNDRED ARE NOT
A single clock is easy to keep accurate. A hundred clocks spread across a station, a hospital or a factory are not. The solution was electrical: one precise master clock that sends a signal to every clock in the building, so that all of them show exactly the same time.
A NETWORK OF ELECTRIC CLOCKS
Networks of electric clocks wired to a precision master clock came into wide use around 1900, in factories, offices and schools. Railway networks and telephone exchanges followed the same principle until well into the age of quartz and internet time.
HOW MASTER CLOCKS WORK
The master clock (in Dutch moederklok, in German Hauptuhr, in French horloge mère) is the only real timekeeper in the system. It is usually a high-quality pendulum clock in a tall wooden or metal case, placed in an office or a technical room.
At fixed intervals, usually every 30 or 60 seconds, the master clock closes an electrical contact and sends a short pulse through the wires to all connected clocks.
The British engineer Frank Hope-Jones refined this principle. In 1895 he and George Bennett Bowell founded Synchronome in London. Their master clock gave its pendulum a small push every 30 seconds with a gravity arm, which was then reset by an electromagnet. At the same moment the system sent an impulse to every receiving clock. The Synchronome system was installed at the Institution of Mechanical Engineers in London when its building opened in 1899.
The principle went further. Building on the Synchronome, William Hamilton Shortt developed a free-pendulum clock in 1921. It was installed at the Royal Observatory in Greenwich in 1924 and remained among the most accurate clocks in the world until quartz and atomic clocks took over.
WHO USED THESE CLOCKS?
WHERE WERE SLAVE CLOCKS AND MASTER CLOCKS USED?
Slave clocks (in German: Nebenuhren) were installed wherever many people had to work, travel or learn by exactly the same time. One master clock in a technical room kept dozens or even hundreds of slave clocks in step throughout a building or an entire site. These are the places where they were most common, and why.
Railway stations
The birthplace of standardised time. Platforms, halls, waiting rooms and signal boxes all had to show the same minute, because a timetable only works if every clock agrees. Double-sided clocks above the platforms let travellers see the time from both directions.
Airports
Departure halls, gates, control towers and offices relied on synchronised clocks to keep flights, crews and passengers on schedule. Large wall clocks were often grouped into world-time displays showing the hour in other cities.
Schools and universities
Every classroom showed the same time, so lessons began and ended together. The master clock often rang the school bells automatically as well, signalling breaks and the end of the day without anyone pressing a button.
Factories and workshops
Shifts, breaks and production lines ran by the clock. Master clock systems were frequently linked to time clocks and punch clocks, so workers clocked in and out by the same time shown on every wall.
Hospitals
In wards, operating theatres and corridors, the exact time mattered for medication, shift changes and medical records. One central system ensured that every department worked to the same minute.
Post offices and telephone exchanges
National postal and telephone services, such as the British GPO, used master clock systems to time sorting, dispatch and telephone traffic. Many of the Synchronome and Magneta clocks still found today come from these buildings.
Offices, banks and government buildings
Town halls, ministries, banks and large office blocks used slave clocks in every room, so meetings, opening hours and the working day ran in step throughout the building.
Broadcasting studios
Radio and television stations depended on split-second timing for live programmes and news bulletins. Studio clocks driven by a master clock made sure every programme started exactly on time.
Shipyards, ports and ships
Docks and shipyards used slave clocks to coordinate shifts and shipping schedules. Larger ships, including naval vessels, carried their own master clock system with slave clocks on the bridge, in the engine room and in the crew quarters.
Military bases and barracks
Where discipline and coordination were essential, one shared time across every building was a necessity. Many robust, plain-faced slave clocks served in barracks, depots and command posts.
Power stations and mines
In control rooms, engine houses and at mine shafts, synchronised time was vital for safety, shift changes and keeping operations running around the clock.
Department stores and hotels
Large stores and grand hotels used master clock systems so that every floor, counter and reception showed the same time, an important detail when opening and closing hours ran to the minute.
Every vintage slave clock once hung in one of these places. Some still carry the clues, such as an inventory number, a company name on the dial or a post office stamp, that tell where they spent their working life.
HOW A SLAVE CLOCK WORKS
A slave clock (also called a secondary clock or impulse clock; slaafklok in Dutch, Nebenuhr in German, horloge réceptrice in French) has no timekeeping mechanism of its own. Open one and you will find no spring, no balance wheel and no pendulum. Instead there is:
1. AN ELECTROMAGNET
A coil that receives the pulse from the master clock.
2. AN ARMATURE
A small metal lever that is pulled by the magnet with every pulse.
3. A RATCHET WHEEL
It moves forward exactly one tooth each time the armature moves.
4. THE HAND TRAIN
It turns that small step into the movement of the minute and hour hands.
With every pulse the minute hand jumps forward: half a minute in a 30-second system, a full minute in a 60-second system. That characteristic jump of the minute hand is the heartbeat of every station clock.
Many systems used alternating pulses, positive and negative in turn. The slave clock's magnet was polarised, so it only moved on the correct pulse. A stray electrical spike could therefore not push the clock forward by accident.
THE SWISS EXCEPTION: THE STOP-TO-GO SECOND HAND
The Swiss railway clock designed by Hans Hilfiker in 1944 added a famous detail. Its minute hand jumps on the impulse from the master clock at each full minute. The red second hand, added in 1953, runs on its own motor and completes its circle in about 58.5 seconds. It then pauses at the top until the next minute impulse arrives. That small pause is the master clock, visible to every traveller.
The Swiss design made the stop-to-go second hand famous, but it was not the only one. Other manufacturers used the same principle, including the German maker Telenorma: some of its TN station and factory clocks also have a second hand that runs on its own motor and waits at twelve for the minute impulse from the master clock. These versions are less common than standard slave clocks, which makes them a welcome find for collectors.
VOLTAGE AND PULSE TYPE
Slave clocks were built for the voltage of the system they belonged to. Common values are 12, 24 and 48 volts, but other voltages exist as well. The coil is wound for that specific voltage, so a 24-volt clock needs a 24-volt pulse to step forward reliably.
Besides voltage, the pulse type matters. Most systems use polarised pulses that alternate between positive and negative, while others send every pulse in the same direction. The interval, every 30 or 60 seconds, must match as well.
If you want to keep the original movement, we make sure the pulse generator matches your clock's voltage, pulse type and interval. For quartz-converted clocks none of this applies: they run on a standard battery.
THE GREAT NAMES IN ELECTRIC TIME
ONE PRINCIPLE, MANY MAKERS
Across Europe, a handful of companies built the clock systems that kept stations, factories, schools and telephone exchanges in step. Their names still appear on the dials and movements of the clocks we restore today, and they are the first thing collectors look for.
GENTS OF LEICESTER (England)
TELENORMA - TELEFONBAU UND NORMALZEIT (GERMANY)
SIEMENS (Germany)
BRILLIÉ (France)
GENTS OF LEICESTER (England)
John Thomas Gent started his business in Leicester in 1872, initially making electric bells. In 1903 the company began developing its "Pul-syn-etic" electric clock system, and in 1907 it introduced the "Waiting Train" master clock. Gents clocks hung in railway stations such as York, in factories, schools and post offices across Britain. Their robust slave clocks, with Bakelite, steel or copper cases, are among the most recognisable industrial clocks today. See for example our 1940s Gents of Leicester double-sided station clock with its factory seals still intact, and our Gent of Leicester slave clock with its original 30-second movement.
SYNCHRONOME (England)
The company of Frank Hope-Jones supplied master and slave clocks to offices, institutions and the British Post Office. A G.P.O. Synchronome slave clock is a direct link to that network.
MAGNETA (Switzerland and Britain)
The Magneta system originated in Switzerland and was adopted by the British Post Office for telephone exchanges and sorting offices. Its master clock was weight-driven. Once a minute a trip gear moved an armature through a magnetic field and generated the impulse itself, with alternating positive and negative currents. Discover our Magneta slave clock and its smaller sibling.
TELENORMA AND SIEMENS & HALSKE (Germany)
In Germany, Telefonbau und Normalzeit (later Telenorma) and Siemens supplied complete clock systems for stations, factories and offices, typically with minute impulses. Their large station clocks, with clean black-on-white dials, are the archetype of German industrial design. See our 65 cm Telenorma station clock and the polished Telenorma TN with its original pulse movement.
BRILLIÉ (France) AND PRAGOTRON (Czechoslovakia)
In France, Brillié built electric station clocks, many of them double-sided, for platforms and halls. In Czechoslovakia, Pragotron became a household name for station clocks, from small slave clocks to large illuminated models. Our double-sided Brillié station clock still runs on its original pulse movement.
THE END OF AN ERA
From the 1970s onwards, quartz clocks, radio-controlled clocks and later network time made the master clock unnecessary. A single wall clock could now keep perfect time by itself. Stations, schools and factories dismantled their systems, and thousands of slave clocks were removed from walls.
WHY THEY SURFACE TODAY
Many were thrown away; the best ones have survived in storage rooms and attics. Every slave clock you find now is a piece of the infrastructure that once ran the industrial world on time.
KEEP TIME WITH HISTORY
Restored station and factory clocks, each one of a kind
ORIGINAL MOVEMENT OR QUARTZ: WHAT SHOULD YOU CHOOSE?
THREE WAYS TO BRING A SLAVE CLOCK BACK TO LIFE
A slave clock without its master clock will not run. There are three ways to bring one back to life:
1. QUARTZ CONVERSION
The original slave mechanism is replaced by a high-torque quartz movement on a battery. The clock runs independently and silently. Ideal for homes, kitchens and offices. A cheap conversion and most times it's possible to convert the original clockhands to fit the quartz movement. So you still have the looks like it did back in the day.
2. ORIGINAL MOVEMENT WITH A PULSE GENERATOR
The original slave movement is kept and driven by a small modern pulse generator that takes over the role of the master clock. You keep the authentic jump of the minute hand and the soft click every 30 or 60 seconds. This is the choice for purists and for interiors where the movement is part of the experience.
3. A COMPLETE SYSTEM
For museums, hotels and collectors: a master clock or controller driving several slave clocks at once, exactly as it was intended. Ask us about the possibilities.
We always state clearly in each listing which option a clock has.
WHAT TO LOOK FOR WHEN BUYING A VINTAGE STATION CLOCK
No two vintage clocks are the same. These are the points that tell you most about a clock, its history and its value.
Maker and dial
Is the brand visible on the dial or the movement? Original dials with maker's names (Gents, Synchronome, Magneta, Telenorma, Siemens, Pragotron) are more sought after.
Size
Small slave clocks of 25 to 35 cm suit kitchens and studies. From 50 cm a clock becomes architecture: it carries a wall in a restaurant or lobby.
Single or double-sided
Double-sided clocks were made for platforms and corridors and are rarer, especially with both original movements.
Case material
Bakelite, cast iron, steel or copper. Each tells something about its era and original setting.
Original paint or refinished
Original paint with patina has authenticity; a fresh finish suits a calmer interior. Both are valid, as long as the seller is honest about it.
Movement
Original slave movement, quartz conversion, or original movement with pulse generator, and in which interval (30 or 60 seconds).
Lighting, glass and hands
Does the clock light up? Does it have the original glass, bezels and hands? Replacements are practical, but should be mentioned.
WHERE A STATION CLOCK WORKS IN AN INTERIOR
A station clock is one of the few vintage objects that works in almost any room.
Kitchen and home office
Here it brings a quiet industrial rhythm, and a large dial that can be read from across the room.
Restaurants and hotel lobbies
A large clock becomes a landmark guests remember, and a natural meeting point.
A world-time wall
A row of identical slave clocks, each set to a different city, makes a wall that tells a story about travel and time. For projects like this we regularly put together matching series.
Furnishing a hotel, restaurant or office? See Furnishing your business or contact us.
FREQUENTLY ASKED QUESTIONS
WHAT IS A SLAVE CLOCK?
A slave clock is an electric clock without its own timekeeping mechanism. It advances its hands only when it receives an electrical pulse from a master clock.
WHAT IS A MASTER CLOCK?
A master clock is a precision clock, usually with a pendulum, that sends electrical pulses at fixed intervals to all slave clocks in a building or network, so that they all show the same time.
CAN A SLAVE CLOCK RUN ON ITS OWN?
Not in its original state. It needs a master clock, a modern pulse generator, or a conversion to a quartz movement.
WHAT IS THE DIFFERENCE BETWEEN A 30-SECOND AND A 60-SECOND SLAVE CLOCK?
The interval of the pulses. In a 30-second system (typical for Gents and Synchronome) the minute hand jumps every half minute; in a 60-second system it jumps once per minute.
IS A STATION CLOCK THE SAME AS A SLAVE CLOCK?
Most station and factory clocks were slave clocks, connected to a master clock. The name describes where they hung; "slave clock" describes how they worked.
CAN I ORDER A MATCHING SET FOR A HOTEL, RESTAURANT OR MUSEUM?
Yes. We regularly have several clocks of the same model and can restore them to one finish. See Furnishing your business or contact us.
FINAL
THOUGHTS
Explore our collection of restored station and factory clocks
A slave clock is a modest object with a large story. It once kept a station, a factory or a telephone exchange running on the same second, and it still carries the click of that era in its mechanism.
Restored and back on the wall, it is no longer part of a system, but the centre of a room.