How a watch works

A mechanical watch is one of the simplest and most beautiful machines in the world. Looking at it through the back of your OFFSHORE Professional chronograph though you could easily be forgiven for thinking it's incredibly complex and involves a little bit of magic going on somewhere.

There is no magic, but what you can see is the culmination of a thousand year journey from the clocks of early Medieval cathedrals to the sophistication and reliability of the 775M2 modified Valjoux movement nestled behind the sapphire glass crystals. This journey has seen the simple machine that measures the passage of time change from cast iron springs and wheels, to brass weights and pendulums, back to springs, across oceans, through the trenches of world war 1 and bombers of world war 2 before settling comfortably onto your wrist.

This page is a short history of that journey and hopefully provides enough information on how clocks and watches work for you to be able to identify and understand the various parts visible in the back of an OFFSHORE Professional. Any errors, omissions or blatant opinions are of course all my own fault.

How a watch works

24 hours in a day

The first clocks were sundials and water clocks, and the first days were divided into 12 hours of work and 12 hours of rest. Around six thousand years ago the Sumerian civilisation of Mesopotamia, in today's Iraq, divided the day up into small pieces and unfortunately they used an incredibly awkward base 12 numbering system to do it. Why they did this when they had 10 fingers like the rest of us is because no one had invented pencils, paper or writing, but very annoyingly had invented tax, so they had to do quite complex arithmetic on their fingers. Sumerian tax was the offerings given to the high priests and temples in an apparently quite regimented system. You can count to 10 on your fingers with modern base 10 numbering, but you can count a lot higher and do some useful maths if you use base 12. I know scholars refer to Sumerian numbering as sexagesimal (base 60) but if you use your thumb to count the parts of the remaining four fingers on one hand you'll see it's based on 12 (duodecimal). To count like this you need to be aware that each finger has three bits to it, bend your finger and you’ll see what I mean. Use the thumb to count the pieces of finger on the same hand and it'll come to 12. If each finger and thumb on the other hand represents a count of 12 then you can quite easy to count up to 60 just using two hands. If this is how you count then it's quite natural to decide a day will be made of 12 hours daylight and 12 hours darkness. And if you're going to divide an hour into something much smaller then it's equally natural to make that 60 parts. You can also do an awful lot of basic maths on your fingers and certainly more than enough to keep a Sumerian tax inspector happy. There's a couple of examples of base 12 maths on the Materials page under the Gold heading (pure gold is '24' carat) and at the bottom of this page as Note 1 if it's of interest.

SundialSundials and water clocks have all but disappeared, but 24 hours in a day, 60 minutes in an hour and 60 seconds in a minute have remained as a good reminder of how it is completely feasible to make things really awkward at the beginning and then be stuck with it forever (Note 1 again).

Moving forward a little, Twelfth Century Europe saw several remarkable advances that set our modern world running. These are pretty obscure when viewed in isolation, such as the introduction of zero into numbering, the change from Roman to Arabic numerals, and paper to write on instead of sheep skin, but combined they allowed reasoning and mathematics to take over from superstition and dogma. The key was mathematics (it might have been religion or enlightenment, but really I think it was just maths and paper), as easier sums allowed people to step beyond simple tool building into working out and designing machines, and the first proper machines were clocks. At the height of the medieval renaissance mechanical clocks began appearing in a few of the fancy new cathedrals that were cropping up all over Europe. These clocks were not terribly accurate but they were far easier and more consistent than relying on the sun shining or trying to get a constant flow of water to the top of a cathedral spire in order to tell the time. The word 'clock' comes from the Celtic 'clocca', meaning bell, so it's likely the invention of a 'ring the church bell so the serfs know it's lunch/dinner/church/home time' machine occurred in the Celtic speaking far west of England, Devon or Cornwall, in the early 1200's. The earliest references to clocks are all from this neck of the woods and the oldest working examples, the Salisbury and Wells cathedral clocks of the 1300's, are in nearby Wiltshire and Somerset. Clock making IS machine making and machine making is the basis of everything in our modern world, so it's not surprising that the steam powered pumps which ignited the industrial revolution also originated in Cornwall.

Ottery St Mary mechanical clock The small Devonshire town of Ottery St Mary has the remnants of a mechanical clock that pre-dates the oldest remaining cathedral clocks by fifty years and was able to track the movement of the sun and moon as well as telling the time, a good indicator that clock making was a refined art by early 1300. Roman Numerals feature on the face because that was the common way of displaying numbers. Arabic notation (1, 2, 3 instead of IV, V, VI) had only made it to Europe in 1202, courtesy of a certain Leonardo Bigollo Fibonacci. The Ottery clock shows the earth at the centre of the dial with the moon and sun orbiting it in line with the belief that the earth was the centre of the universe.

Despite being in deepest-darkest-remotest Devon, Ottery had a grammar school that was established by the same John Grandisson that commissioned and installed the clock in the newly built church. Schools were rare in the 1300's, but were an absolute necessity for teaching the Latin needed to read books, and the geometry and mathematics required to design cathedrals, churches and clock mechanisms. Grandisson's school and church were part of a larger monastery that was dissolved by Henry VIII a few hundred years later, and although the monastery is long gone the clock remains in the old church. The school moved half a mile up the road and was renamed The King's Grammar School after its new benefactor, and there it continued its high academic standards for many centuries. I'm using the past tense for the school though as in 2011 it was re-branded as a 'sporting' academy, which is a good sign it's probably slipped a bit on the academic front. Anyway, this is the school I went to and the unfortunate fact that previous pupil Samuel Taylor Coleridge's romantic poetry was high on the syllabus is one of the reasons I became an engineer and went to work in the oil industry.

Old churchThere are hundreds of old and sometimes neglected 11th and 12th century churches across Devon and Cornwall and I suspect one of them houses a rusty old machine, tucked away in a corner and long forgotten about, that'll turn out to be Genesis, the original Mark 1 Clocca. If you're ever in these counties then it's always worth stopping at any particularly run down old church to have a hunt around. You can spot if a church is from the right period because it will have a small and irregular sandstone block construction and a clock tower that looks a little like a castle battlement - dual use Norman architecture at its finest. The picture to the right shows the clock tower for Venn Ottery church which was built in 1085. An ideal candidate, but no old clock - I've checked.

Tick-tock, the mouse and the clock



The only problem with the swinging pendulum of course, is that is will come to a halt if you leave it alone, so to keep it running you need to keep giving it a little nudge. The nudges don’t make it run slower or faster, because as Galileo discovered and we've just proven, as long as the pendulum stays the same length it will always take 1 second per swing.

You can sit at your computer flicking the dangling mouse all day if you like, but you’ll soon become bored and try to think up a way of automatically giving it a nudge, which now makes you an engineer. The best way of automatic nudging is having the pendulum bump against a lever at the end of each swing that gives it a flick. We can make a lever do this by loading it with a ratchet gear and heavy weight. When the pendulum pushes the lever it lifts up the ratchet and allows the weight to drop a little, the weight is tied to the lever so as it drops it pushes back quite hard. As the lever returns to it’s starting point the ratchet falls back into position and stops the weight from dropping any further. It looks like this:




Clock exploded diagramIn a grandfather clock the lever that pushes the pendulum and counts the swings is called an anchor & pallet, and the ratchet wheel it operates is called an escape wheel. The whole thing together is referred to as the escapment. If Christiaan Huygens had been British rather than an Huguenot Dutchman he would have called it a lever & ratchet drive and it would be altogether less glamorous that the evocative sounding escapment.

Once they understood how an escapment worked then anyone with a little metal working skills could build a clock, and indeed by the end of the 1600’s there were hundreds of clock makers all over Europe. Copper and brass were the most popular metals to use as they were relatively cheap, easy to work and didn’t rust. Over in North American, where metal was more scarce, the clockmakers regularly used wood to make their grandfather clocks, so if you come across a knackered old wooden movement clock in an American auction then it's worth a good inspection.


Grandfather clocks to Marine chronometers

In the late 1600’s and early 1700’s the greatest nation of all time, and the country that had just invented the industrial revolution, was flexing it’s muscles and reaching out to civilise the heathen masses. There are many reasons Great Britain came to dominate the world, most of them to do with the industrial revolution, a god given arrogance, and the utter ruthlessness that is hammered into us and honed to perfection on the playing fields of our youth. (Note 2, bottom of page, and as an aside if you add good manners and politeness you can understand why British actors are always the bad guys in Hollywood movies). One of the less well known reasons though was because we generally knew where we were. Knowing where you are when sailing across oceans is important to avoid accidentally running into something big and solid like an island, and the subsequent sinking with all hands that inevitably followed in an era where no one had learned to swim.


Longitude, how far East-West, can’t be done by looking at the stars or the sun though, because they move across the sky as the earth rotates. To know your longitude you need to know what the time is back at home, and specifically the time in Greenwich just to the East of London and the home of the Royal Navy. If it's March 21st, your little book of tables shows that the sun rises in Greenwich at exactly 6.00am. On your ship somewhere in the Atlantic you have a clock set to Greenwich time and when the sun rises it's showing 7.00am. You now know you're 1 hour behind Greenwich. There are 4 time minutes in a degree (Sumerian maths again), so 60 minutes means you’re 15 degrees West of London. This puts you a little way out from the edge of Ireland, so it’s time to keep an eye out for their rocky shoreline.

Knowing the exact time in Greenwich is the issue. And here the problem with putting a grandfather clock and its swinging pendulum on a small sailing ship becomes obvious. The pendulum had to go, and it was an Englishman that figured out how to do it in a way that made his clock incredibly accurate no matter how rough the sea was. John Harrison’s marine chronometer of 1736 replaced the swinging pendulum with weights that bounced backwards and forwards on springs.

The balance wheel



Balance wheel viewBalance wheel

+ and - above adjusts the length of the hairspring to allow timing to within a couple of seconds a day. Exactly the same principle as adjusting the length of a grandfather clock pendulum.

The main spring

The final part of marinising a grandfather clock is to get rid of the heavy weight that drops a little with each tick. As you can imagine, the weight can upset the increasingly delicate machinery of the clock. Removing the weight turned out also to be a simple case of swapping it for another helical spring. Rather than a spring that oscillates, this helical spring is wound up nice and tight and then the force it exerts as it slowly unwinds is used to give the little sustaining pushes at the escapement that keep the balance wheel running. Because it’s the spring that powers the whole clock it’s called the main spring.


Pocket watches to wrist watches



Pocket watches, as their name implies, were kept in a pocket, and to prevent them accidentally falling out and being lost they were tied to a suitable button hole via a long chain. Normally the pocket used for the watch was on a waistcoat, but as waistcoats became less fashionable the pocket transitioned to the trousers. If you’re wearing a pair of jeans then take a look at the right hand front pocket. You’ll probably notice a much smaller pocket sewn inside it. That’s a design hang-over from the first jeans of around 1880. It’s on the right because normal people are right handed, but I expect somewhere in this world you’ll be able to buy a pair of left handed jeans if you want.



1923 saw the first patent for a self winding complication in a wrist watch. Given that the wrist moves around a lot, it was a natural development to use the movement as a good way of automatically winding up the main spring. Self winding is achieved by having an offset weight on a wheel that moves around with the motion of the watch, winding up the spring. The self winding rotor can be clearly seen through a glass backed case and, as with the Field Engineer, is often engraved or customised to a particular watch manufacturer.

OFFSHORE Professional In Samd


In the late 1960’s and early 1970’s automatic winding was incorporated into chronograph watches with the launch of the Chronomatic (1969), Seiko 6139 (1969), Zenith El Primero (1969), Lemania 5100 (1973) and finally Valjoux 7750 (1974). These movements are either integrated chronographs, meaning the stopwatch is built into them, or have the chronograph added as a module to a more basic movement. Integrated chronographs are inherently simpler, which means they’re more robust and better timekeepers. The button layout for these movements also standardised to the familiar top button for start/stop and bottom button to reset to zero.


The Quartz Era

Just as the mechanical watch was reached perfection, an entirely new way of calculating time firmly pulled the rug from under the feet of the established watch industry. The battery powered quartz watch. Explanation as to how quartz watches work is included in the Watch Terms page on this website, but suffice to say a quartz watch is 10 times more accurate and 100 times cheaper to make than the best mechanical chronograph.



Today’s mechanical watches



Just like cars and architecture, by looking at which models and styles have lasted through the fads, you can work out what the perfect man’s watch should look like. Omega Speedmaster of course, Rolex Submariner, Cartier Tank, they were all perfect from the start and have outlasted flared trousers, big hair, manly stubble and hopefully exposed underpants. Classical styling with a slight edge to it appears to be the best way of ensuring longevity; Bauhaus with just enough art nouveau to avoid that 1960's town planner trap of brutalist modernism. There's a trick in making things look nice and balanced known as the fibonacci sequence number pattern, as described elsewhere in this website. The trick is that it generates sizes and layouts that look appealing to us because the sequence features in many natural forms, so not only are we instinctively familiar with it but since large parts of us feature it we're hardwired to find it very comfortable.

Future developments




Looking at an Apple 1 in 1976 and imagining what personal computers would do in the future you’d probably come up with word processing and a game of space invaders. An early president of IBM is often quoted as saying he could see a world market for possibly 5 computers. That’s five, not 5 million, but 1, 2, 3, 4, five. Just the other day driving to Cornwall we had more than that running in the car. One child was watching Merlin being continuously streamed onto a seat back display, another was snap-chatting with friends and occasionally using gps to plot location, time to destination and ground speed, ‘mum, dad's going way too fast again’, and mum was looking up things to do that would have more association with bracing walks than computer screens. Add in a computer running the engine management, one in the dashboard doing the map reading and various phones and it makes quite a lot.



In fact the only thing tomorrows 3D printers won’t do is make you an OFFSHORE Professional Field Engineer with serial number 007 on it. I’m afraid I made and sold that watch a long time ago and I can guarantee the electronic files I might sell in the future won’t replicate it, or indeed any of today’s Field Engineer Chronographs. They will remain completely unique and completely special; products from the peak of hand made chronograph manufacturing.

Note 1:


Note 2:

Royal Navy officers of the time could be severely reprimanded for 'following orders'. Adapting to situations, taking the initiative and ignoring orders that were counter productive or dishonourable was standard operational procedure. The same officers could also be reprimanded for 'insufficient agression', with one poor Admiral actually being executed for the offence.  These policies led directly to the default positions of 'always attack regardless of superior forces' and 'attack is the best form of defence'; philosophies that continue through to today in all of Britain's armed forces and make them the most agressive and formidable foe. Many schools though, appear to have adopted non-competitive sports, which I think might be a bit of a mistake.