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.
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.
Sundials 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.
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.
There 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
If you’ve got a minute to spare, then look around you for something on a piece of string or wire. Since you’re reading this on your computer why not try the mouse. Hold it dangling down by the wire, give it a small push and it will quite happily swing from side to side. If you shorten the length of wire you’ll notice each swing takes less time, and if you lengthen the wire you’ll find each swing is a longer duration. With a bit of experimenting you’ll find the exact length needed to get one swing per second. You’re officially a scientist now, because you are observing and experimenting with natural phenomena. Interestingly if you start with a really big swing and let the mouse swing away until it comes to a stop you’ll notice that each swing always takes exactly 1 second. It doesn't matter if it’s the first big swing or the last titchy swing, they all take exactly the same amount of time. What you have with your swinging mouse is the perfect time regulator. It’s the part that was missing from medieval clocks and it was by far the best discovery of 1581. Italian scientist Galileo Gallilei first noticed this constant period of swing observing the swaying chandeliers at the University of Pisa.
The swinging pendulum is the heart of a grandfather clock. By ever so slightly increasing or decreasing the length of the pendulum you can speed up or slow down a grandfather clock to an incredible accuracy, and easily to within 10 seconds a day. Given that a 24 hour day has 86,400 seconds this represents an almost dizzy level of accuracy of 99.99%.
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:
So now we can have a pendulum that will swing at 1 second intervals all day long.
Unbelievably it took almost 100 years for someone to work out how to keep a pendulum swinging, but in 1654 Dutchman Christiaan Huygens used this method to invent the worlds first pendulum clock.
Counting up the swings, which is really what a clock does when it tells the time, is the easy bit as each flick of the lever also knocks a second hand forward by one space. Each time the second hand makes a full rotation of the dial it in turn nudges a minute hand forward one space, and of course a full revolution of the minute hand will advance the hour hand one space. All the complex looking dials and gears you see in watches and clocks are just ways of making the minute hand turn 60 times slower than the second hand, and the hour hand turn 24 times slower than the minute hand.
In 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.
In the modern world it’s perfectly feasible to make a grandfather clock from plastic. I have no idea why Lego don’t sell a kit for this, because it would be an excellent thing for them to do and would be a guaranteed best seller as presents from grandparents. ‘Oh thanks granddad, a Lego clock that I have to build myself.’
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.
There are two parts to working out where in the world your little ship is; how far North or South you are and then how far East or West. The North South bit is quite easy as it’s done by looking at stars. If the pole star is directly above you then you’re at the North Pole (and in trouble). If it’s just visible on the horizon then you’re at the equator. Measuring the angle of the pole star from the horizon, or the midday sun using a sextant, gives you a very accurate latitude position.
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
To understand how bouncing weights on a spring work it’s necessary to dig out a 30cm plastic ruler from the draw in your desk. Hold the ruler onto the desk with most of it sticking out over the edge and flick the end that’s hanging out. The free end bounces up and down. Just like a pendulum, if you shorten the amount of overhang from the desk the bounce is quicker, and if you lengthen the overhang the bounce is slower. Also, just like a pendulum, with the overhang a fixed length each bounce will take exactly the same amount of time as the one before, big bounce or small. Your ruler is acting like the oscillating spring in John Harrison’s marine chronometer.
Obviously the ruler is bouncing a lot quicker than the mouse was swinging, but if you made it long enough you’d find the point at which it bounces exactly once a second. It turns out that the best way of making a length of metal long whilst still being nice and compact is to have it curve around on itself in a big spiral. Another good way to slow the bounces down is to add a weight to the end. On the end of a curved around, spiral spring, a big weight can be made in the image of a bicycle wheel rim that turns clockwise and then back in an anti-clockwise direction. If the wheel is only allowed to oscillate clockwise and anti-clockwise by being fixed to a bearing at its middle it’s ruggidability improves immensely. Because it looks like a wheel, is nicely balanced, and was a British invention, it’s called the balance wheel. The balance wheel is clearly visible through the back of a Field Engineer chronograph:
+ 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.
With a few more modifications to account for metals expanding and contracting in different temperatures, the marine chronometer came of age and with it the grandfather clock evolved into a mobile timekeeping device.
Pocket watches to wrist watches
A clock made with a real bicycle wheel as a balance wheel is perfectly feasible, and a bit like the Lego clock in that I’m surprized there isn't one already available. The real advantage with a balance wheel though comes when it’s made much, much smaller, say just 1cm across. The helical spring can then be as thin as a human hair, cunningly now called a hair spring, and the whole clock can be miniaturised to the point it will fit comfortably into your pocket.
Balance wheel based pocket watches appeared in the 1700’s. Before then the few portable watches had been scaled down versions of the early cathedral clocks and were so inaccurate that they never bothered with a minute hand. ‘My pocket clock say's 11 am but my stomach say's lunchtime so it’s probably about lunchtime’.
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.
By the early 1900's Europe had realised that in order to compete with the emerging dominance of the US on global markets it would need to copy their mass manufacturing techniques. Combined with the impressive production ability of the new US watch companies, this meant that the pocket watch became sufficiently cheap that many people, and most army officers had one. The early 1900’s also saw the transition of warfare from a noble venture performed on horseback with gallant charges in bright red uniforms into the mechanised killing we associate with the trenches of the Western front. In this new type of warfare it paid to keep your head down and stay as close to the wet and muddy earth as humanly possible. This presented quite a hazard to the pocket watch as the chain would get caught on everything you crawled over and the watch was often wet and grimy. It was also damned tricky to pull the watch out to check when ‘zero hour’ was. The pocket watch not surprisingly transitioned to the wrist, first under the name trench-watch and then as the common wrist-watch. One early wrist-watch design by Cartier is even named after the metal monsters that Britain used to finally start breaking through the German lines in 1917; the Tank.
As watches became ever more popular and cheaper, they developed a tendency to stay attached to the owners wrist no matter what he or she was up to. This drove the development of robust movements, waterproofing, luminescent hands, cold temperature lubrication and even slide ruler bezels. Miniaturisation also allowed watches to become more complicated than just time telling machines. Day of the month, day of the week, chronograph (a built in stopwatch), 24 hour dials, moon phases and numerous other complications were introduced. The chronograph is my personal favourite, although I’m also quite partial to moon phase. Not being a werewolf though I can’t justify building a moon phase watch.
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.
Automatic watches have two big advantages over manually wound watches; three if you include the obvious 'forgot to wind it up' advantage. Because an automatic watch spends much of its time fully wound, the torque from the mainspring is constant and so time keeping is better. Secondly, since you don't have to turn the crown 20 or 30 times each evening to wind it up there is much less wear on the crown seals and so water and dust resistance are also far better.
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 fully integrated automatic chronograph is, in my mind at least, the ultimate mechanical wrist-watch movement. 40 years after their introduction, many other people must think the same as the best of these 5 movements are still in production.
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.
Under this technical and financial superiority mechanical watches almost disappeared off the face of the earth. Around 100,000 Valjoux 7750 movements were made in 1974, but in 1975 the production line was stopped and the machinery and dies put into storage. Such was the drop in demand for mechanical watches that movements made in 1974 were still being used in new chronographs up to 1980.
By the mid 1980’s though the fad for quartz watches was waning. Some owners disliked the way the battery would run out at the worst possible moment, others disliked the cheap casing and straps that went hand-in-hand with a cheap mechanism, but most simply realised that they wanted something a little more special. A watch and a wedding ring really are the only pieces of jewellery that a man can wear, and since the wedding ring has to be a plain band, the only real choice is in the watch. As decisions go it’s right up there with type of car and model of wife in importance.
Today’s mechanical watches
Watch fashion comes and goes, sometimes slim and minimalist, other times bright and blingy. Today I feel we’re in a bit of a blingy phase. Gold, diamonds, bits of mechanism visible through the dial, weird and wonderful ways of displaying the time, all black including black hands on black dials. They’re all great of course, and each to himself is my motto, although I have to admit to not being over keen on the mechanism showing through the front dial. I know it’s done so that casual on-lookers will know you're wearing an expensive mechanical masterpiece, but every time I see it I have to check if the owner is also showing the top of his underpants as well so that everyone knows he wears Calvin Klein boxers.
A proper watch is an expensive purchase so you really want it to last, not just mechanically but aesthetically as well, and this means trying to avoid fashions. Google ‘the Bay City Rollers’ if you don’t know quite how embarrassing it is for today's parents to show their children the fashion of that era. Imagine then if your grown up son in 20 years time wants to wear his dad’s old watch. ‘Oh, it’s a Breitling Mulliner, thanks dad but I think I’ll skip it’.
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.
We’re at the start of a 3D printing revolution that is going to have a profound effect on manufacturing and the way we buy products.
The computer and internet billionaires have all be made, so if your looking to be fantastically rich then that’s a boat that already speeding over the horizon at 40 knots. State of the art 3D printing though is more basic today than an Apple 1 was in 1976, and it also has a lot more obvious uses than the Apple 1 could boast. If you want to make a fortune then 3D printing is a boat sitting at the dockside with its engines warming up.
Imagine a machine next to the oven that can make you a new pair of shoes, perhaps special lacrosse boots for your new found hobby or some trademark Christian Louboutin red soled stilettos for your wife to wear on a night out. The same machine will also make a motorised scooter to get you there, or even a Ferrari GTO complete with V12 engine, and tailored to your exact body size if you have a garage sized printer. We're not talking about it making the parts that you then need to put together, this future machine will print a working car with an engine from the ground up. Working at a molecular level, it will also print you a lamb kebab to scoff on when you get back from all that old fashioned ‘hand made’ food you had to wait ages for at the fancy restaurant.
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.
3D printing is going to be able to manufacture goods and machines smaller and more complex than we can possibly hope to do today, right there in your kitchen. It’s going to open a whole new world of manufacturing that will affect every strand of our lives and will even revolutionise the computer industry as microprocessors become fully 3 dimensional instead of layered wafers of silicon on top of each other. Forget the power of quad core microprocessors, think more 128,000 core or 4 giga-core machines.
With these possibilities in mind watch manufacture is obviously going to be one area that changes completely. Instead of selling someone a ready built watch I might sell you the files for your personal printer to run one off in your kitchen. Special date engraved on the rotor?- an instant change and not a 3 month wait. Want it 20% smaller and in the same tone of red as those shoes, well the files are yours so just ask the machine to run you off a special for the big night out. When you've finished drop the watch back in the machine and it’ll deconstruct it so the materials can be used again tomorrow.
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.
Sumerian mathematics: Our modern base 10 numbering system has two factors; 5 and 2 which are both primes. A duodecimal (base 12) system however has 6, 4, 3 and 2 as factors, two primes and two non-primes, including the number of sides to a square and a cube (useful features if you're a farmer with a rectangular field and a tax system based on volume of wheat). Once you get the hang of it, counting in base 12 on your fingers is easy and allows a lot of mathematics including fractions (the factors) to be done without having to use a pencil and paper. Base 12 lives on not just in time, geometry and co-ordinates, but also in our language and other measurements.
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.