Historical Developments in Precision Timekeeping

This is not an authoritative guide. It may not even be very accurate. I am just trying to lay things out as I understand them, so as to try to sort out what I think I know and make some sort of record of what I think I have learnt, before I forget everything and get myself too muddled. I shall no doubt have to re-visit this page and make corrections, from time to time.


Long before the earliest clock that we know of, people tracked the passage of time. And if we believe that neolithic structures such as Stone Henge were deliberately constructed so as to align to celestial events, then our ancestors appear to have been able to track the passage of time with considerable accuracy. We can only guess at the lengths to which our ancestors went, but it is clear that the act of tracking and measuring time has long been of very great importance to mankind.


At some point in the depths of time, a clock was invented. The science of horology is the pursuit of ever more precise and dependable measurements of time. At least, that's what the word truly means. For a long time, horology has also encompassed the decoration and elaboration of timepieces. A viable, functional, dependable clock was, after all, an achievement worth boasting about. By and large, however, it was the accuracy of a clock that defined a clock-maker's place in history.

Compared to the apparent pace of progress in our modern, technological world, clocks seem to have taken ages to get anywhere. I'm no expert on clocks (let's face it, I'm no expert on anything), but I have heard it said that clocks of old could be very, very accurate. Pendulum mechanisms and grasshopper escapements and all sorts of clever thinking could render a mechanical clock as accurate as you'd likely ever need. Someone recently built a 'Longitude' clock from John Harrison's eighteenth century design and it entered the Guinness Book of Records for losing only five eighths of a second in a hundred days. That would work out at less than 2.3 seconds per year.


In a world already fast being shrunk by trade and conquest, the ability to accurately navigate at sea would free ships from the need to sail relatively close to shore. Accurate navigation, and with it the ability to take more direct routes across large tracts of open sea, depended on having a highly accurate and highly consistent time-keeping device. But, transferring the accuracy of a large, stationary clock into a small, mobile package was, apparently, an enormous challenge. Without a pendulum and a rock-steady platform, the mechanism would need springs and a design that would work no matter which way up it was or what forces of motion were applied to it.

This isn't the place to try to lay down a history of mechanical watches, so suffice it to say that a fairly wide variety of escapement designs were tried and the one that came to dominate the modern world of wristwatches - the Swiss lever escapement - was not necessarily the most accurate, but did display good accuracy, robustness and reliability that gave it the competitive edge.


Today, the Swiss lever escapement is found in almost every mechanical watch from every major watch producer except for Omega. Small, independent brands occasionally come up with something new. Top, high-end brands occasionally come up with an interesting prototype or an unbelievably expensive limited run of watches that incorporate something other than a Swiss lever escapement. But the industry, from small players to large, is locked into this one particular movement. And pretty much for the same reasons that led to the Swiss lever escapement's rise to popularity several hundred years ago - it's reasonably accurate, sturdy and dependable.

Reasonably accurate... Therein lies the 'tell'. The statement that reveals that the core focus of the majority of watch-makers has shifted, inescapably and irreversibly, away from true horology. Two or three seconds per day is accurate enough. You can't compete with quartz, so there's little point trying to push the 'accuracy' angle. Better focus on design, complications, craftsmanship. Better sell it like it's jewellery. There are mechanical watches, now, with moonphases so accurate that it will be over two million years before they are off by as much as a day. But they still can't promise to keep time to better than a couple of seconds per day and any fancy new developments that may from time to time emerge in making mechanical watches more accurate, are all rather like trying to squeeze one or two extra miles per hour out of a steam train.

So, I won't dwell on the modern mechanical watch for very long, but I will mention some notable developments that have contributed to making today's clock-work watches better time-keepers than their predecessors.


Omega's version of the Daniels co-axial escapement was not intended to deliver greater accuracy than a Swiss lever escapement, but to reduce wear and to improve longevity of the movement and consistency of function. With the move to silicon balance springs in their Master Co-axial version of the escapement, Omega have raised the game a notch. Rolex have moved to using Parachrom hairsprings and Paraflex shock absorbers to make movements that are both strongly resistant to the effects of shock and magnetism and that deliver more consistent performance over time. Sinn's Diapal approach removes the need for oil in the escapement, and in so doing removes one of the key maintenance areas of any mechanical watch.

Not more accurate, then, but more reliable and more consistent. And that is a key component of a high accuracy watch. There is no point in having the world's most accurate movement if it can maintain that accuracy for only a week before needing to be serviced.

Beat rates

One thing that used to signify a high-maintenance watch was a high beat rate. Modern lubricants, new alloys and very high precision engineering have made it easier to produce reliable high beat movements. Once considered to be 'high beat', 28,800 bph movements are now rather common. So, why choose a higher beat rate anyway? Smaller, faster-rotating balance wheels are said to be harder to disturb than larger, slower wheels, and this reduction in sensitivity to external mechanical forces is believed to give high beat movements the advantage in maintaining accuracy.

36,000 bph is considered 'high beat', today, although there have been movements with much higher beat rates than that. Grand Seiko is particularly well-known for 36,000 bph movements, but they also produced a less-well-known 43,200 bph movement under the 'Credor' brand in 1998 (the GBBX998).

Electric watches

Many years earlier, Citizen had also produced a 43,200 bph watch in their 'Cosmotron' line of electric watches. Electric watches date back to a time before quartz, when watch-makers still vied to create the most accurate timepieces possible. Starting with Hamilton, in America, electric watches began to emerge in the late 1950s but although they are seen as an important development in wristwatch technology, the addition of an electrical drive unit did nothing, by and large, for the accuracy of the movements.

Tuning forks

Tuning forks, however, were a whole new ball game. Coming not so long after the advent of the Hamilton Electric 500, Bulova released the world's first tuning fork watch in October, 1960. The wristwatch's beat rate had suddenly shot up to 360 Hz as a metal tuinng fork was vibrated under the influence of electromagnetic impulses. Those vibrations were translated directly into drive for the hands, resulting in an incredibly smooth progression of the second hand around the dial. Adjusting the rate of the watch was achieved by adjusting the balance of the tuning fork. Aesthetics of a smooth-gliding second hand aside, the tuning fork watch claimed to be able to deliver accuracy of a minute per month and with that claim it blew every other type of watch out of the water for the next decade.

Several manufacturers jumped onto the tuning fork band-wagon, and different movements featured 300 Hz, 360 Hz and 720 Hz oscillators. Omega's 720 Hz Megasonic was released in 1973 - well into the quartz era and just one year before the company released their 2.4 MHz quartz Marine Chronometer. In fact, both tuning fork and electric watches continued to be produced by several companies right through the early years of quartz.


When quartz watches came along, it wasn't as if the game was over and all other types of watches ceased to be produced. The earliest quartz watches were incredibly expensive and somewhat delicate. They had been developed, however, because it was seen how good larger quartz clocks were and bringing such accuracy to a wristwatch was an obvious and logical step. From a piece of metal vibrating at several hundred hertz, the horological world moved on to quartz crystals vibrating at several kilohertz. Today's standard quartz frequency is, of course, 32 kHz, but this was not the case in the beginning.


The first quartz watch on the market in 1969 (the Seiko Astron 35SQ) had an oscillator frequency of 8 kHz (8,192 Hz). A month later, in January 1970, Seiko released an updated version with a 16 kHz (16,384 Hz) oscillator. Later the same year, Omega became the first Swiss watchmaker to release a quartz watch, with its iconic Electroquartz being the first to feature the CEH consortium's Beta 21 movement (re-packaged as Omega's cal. 1300), which also used an 8 kHz oscillator.

In 1971, Seiko launched the V.F.A. 38SQW. Besides the frequency of the oscillator, this may be considered to be the first quartz watch to exhibit all the features that you will find in today's timepieces. As with the updated 35SQ, the 38SQW used a 16 kHz oscillator, cementing Seiko's move away from 8 kHz movements. Not far behind Seiko, Girard Perregaux released the cal. 350 which also featured all the various attributes of modern quartz watches and upped the game a notch by sporting the world's first 32 kHz (32,768 Hz) oscillator.

Meanwhile, through the continued run-out of the CEH group's Beta 21 movement, 8 kHz oscillators continued to come to market in watches by Rolex, Zenith, IWC, JLC, Longines, Rado, Bucherer, Bulova, Piaget and Patek Philippe. With GP the only one to feature a 32 kHz oscillator, and Seiko doing their own thing with 16 kHz, it was by no means clear, in the first couple of years of the 1970s, that 8 kHz watches were living on borrowed time. By 1975, however, oscillator frequencies had hit an all time high.

Let's remember that in 1973 Omega were still releasing tuning fork watches. Quartz was not yet the only player in town. But regardless of the innards, it was clear that (in some quarters of the watchmaking world, at least) there was a focus on developing higher frequency movements. Omega's 1973 Megasonic took tuning fork movements to an unprecedented 720 Hz, and in 1974 the same company released the world's first quartz watch with an oscillator in the MHz range - the 2.4 MHz Omega Marine Chronometer. Wristwatch accuracy was now rated to just one second per month. In Japan, Citizen was also working on a high frequency quartz oscillator and in 1975 they released the Crystron 4 Mega, sporting a 4.19 MHz oscillator. The boast, at the time, was that the 4 Mega would hold to three seconds per year. Only very, very recently, with the advent of atomic watches and self-calibrating thermocompensated movements has any manufacturer promised a tighter spec. than that.

By the late 70s, electric and tuning fork watches were out, and quartz was in. But approaches to improving accuracy were still far from settled. Citizen continued to produce 4 MHz watches for several years, and Junghans jumped on this band-wagon in 1978, with Casio following suit in 1980. But by that time, things had moved on. In 1977, a year before Junghans released their MegaQuarz, Rolex brought to market the world's first movement to feature both rate adjustment and thermocompensation (the Oysterquartz cal. 5035).

VCTCXO (voltage controlled temperature compensated crystal oscillator)

As immune as they may be to the vagaries of motion and of gravity, quartz crystals nevertheless face a very significant challenge to their ability to maintain a steady rate of oscillation and that, of course, is temperature. The frequency at which a quartz crystal oscillates, at a given voltage, varies depending on its temperature. Up until 1977, most quartz watches were simply treated to fine rate adjustment at a set temperature in the factory. With a little patience, a very finely adjusted movement could probably be relied upon to keep to within a few seconds each month. This was far better than any mechanical or tuning fork could promise, and may well have been more accurate than most people would have considered necessary. The trouble is, that even a very finely adjusted movement could only deliver consistent high accuracy performance if it was treated to consistent, fairly narrowly-defined climatic exposure.

By using high frequency oscillators, Omega, Citizen, Junghans and Casio had sought to create movements that were simply less sensitive to temperature fluctuations. The high frequency approach, however, had its drawbacks. The most obvious problem with using a MHz-range oscillator would, of course, be battery life. Beyond the practical considerations, however, I also think there may have been a sense that high frequency movements were a bit stuck-in-the-past. Besides the higher frequency oscillator, these movements were much like any other of the mid-70s and did not reflect the pace of change in the world of microelectronics. Even Casio's digital 4 MHz watch was nothing particularly new. Digital watches had been around for years, and Casio's high accuracy offering in 1980 was both too late to capitalise on the high frequency band-wagon, and too expensive for what was, in all other respects, a rather ordinary timepiece.

In 1977, Rolex redefined 'state-of-the-art' in quartz watches, with the release of the Oysterquartz and the world's first movement to feature both a rate trimmer and thermocompensation. Without suffering the same impact on battery life as MHz watches had seen, the Oysterquartz could deliver consistent high accuracy regardless of changes in climatic conditions. It did this by measuring the one variable that it couldn't adjust - the temperature - and adjusting the one variable that it could - the current supplied to the oscillator. In this way, the counting circuitry simply had to keep counting a steady 32 kHz oscillation, while the current fed to the oscillator was varied by comparing its temperature (as measured by a nearby thermistor) against a record of its pre-established thermal performace. And if you're surprised to learn that Rolex was once producing the world's most advance quartz watch, you may be even more surprised to learn that they once even developed an LED watch.

Today, it is suspected that Citizen and possibly also Seiko use the VCTCXO approach (or perhaps some variation on the theme), although their precise methods are not clearly documented.

Twin quartz & dual oscillator

In 1978, Seiko's response to the advent of thermocompensation was their Twin Quartz range. Seiko's approach differed from Rolex's in two ways. First, instead of using a thermistor to measure the temperature, Seiko used a second quartz oscillator. Second, instead of adjusting the frequency of the oscillator, Seiko adjusted the count.

It is not 100% clear from the documentation, but it appears that some Twin Quartz movements may have employed two oscillators of the same (32 kHz) frequency. The idea seems to be that these oscillators are somehow slightly different and have different thermal performances. This being the case, the frequencies of the two oscillators will change at different rates, as the temperature rises (or falls). By measuring the difference between these two rates, the movement's circuitry can determine the temperature which the oscillators are experiencing. Once the temperature is known, the movement's circuitry compares it to the pre-established thermal performance of the main oscillator, and instructs the count circuitry to deduct an appropriate value. For example, the frequency of a slightly cool oscillator may not be 32,768 Hz, but, say, 32,780 Hz, in which case the count circuitry should be instructed to deduct '12' from its count. The count circuitry then sends a pulse to the stepper motor to move the hands at pretty much exactly the right time.

Now, having just given that example, I am very conscious that the numbers are likely to be way off the mark. There are aspects of the mathematics of quartz watches on which I am simply not up-to-speed. It could be that such small changes cannot be adjusted for due to the way in which count is divided (remember, a count of 32,768 must be divided down to just one tick per second). But anyway, I think the basic idea, as I have presented it, is sound.

Even if some of Seiko's Twin Quartz movements may have used two 32 kHz oscillators, others clearly did not. The 9442 draws half a microamp more power than the 9923, using the same battery (ref. Seiko Battery List). While the 9923's documentation is less than 100% clear about the frequency of the auxiliary oscillator, the documentation of the 9442 clearly states that the auxiliary oscillator for that movement has a frequency of 40 kHz (40,960 Hz). The documentation for the 10 SPY cal. 9943 and the 5 SPY cal. 9983 is missing, but the power consumption and battery life for these two movementts are almost identical to those of the 9923. So, on the balance of probability, I believe that the 9943 and 9983 most likely have 40 kHz auxiliary oscillators. The use of a higher frequency auxiliary oscillator no doubt has a direct impact on battery life, but it may offer more accurate temperature measurement.

It is clear that Seiko's approach produced watches that were far more accurate and far cheaper than Rolex's Oysterquartz, but I believe there was a fundamental flaw in the Twin Quartz concept: crystal ageing. As a crystal oscillator ages, its thermal performance changes. If your watch has a rate trimmer, then you can adjust for this. But if the accuracy of your watch depends on knowing the thermal performance of not one but two crystal oscillators, then you're in trouble. On the circuitry of each Twin Quartz movement are two trimmers: one for the main oscillator and another for the auxiliary. Seiko's technical manuals advise those servicing Twin Quartz watches to touch only the trimmer of the main oscillator and under no circumstances to touch the other! The intrepid watch-fixer is further advised that, prior to attempting regulation, he should use a Seiko QT-99 to determine the rate of the watch. If its rate falls outside of a reasonable range, then replacing components, rather than regulation, is advised. To me, the message is clear: the second oscillator is a problem, and once it has drifted too far off the mark, efforts to trim the rate via the main oscillator are futile. The best you could hope for is to bring the watch back to delivering a good rate at a given temperature. But once the effects of ageing have truly taken their toll, the circuitry is going to be applying all sorts of erroneous count 'corrections' every time the temperature rises or falls. So, unless you keep your watch in a temperature-controlled oven, you have no hope of seeing the original factory SPY values again.

So, that settles it, then. Thermistors are the way to go. Except... the watch that is currently performing best in my collection is a dual oscillator Longines. Most of what I know about this, comes from one particular thread on the WUS HAQ forum, which would date ETA's dual oscillator movement to the late 1980s. I believe Seiko had given up on Twin Quartz watches by the mid-80s, and as far as I can tell, ETA didn't stick with the concept for very long. So, how come the Longines is keeping such fantastic time when my amazing cal. 9983 Seiko SQ has slipped from its 5 SPY factory spec. to 271 SPY, today? The Longines may well have had its rate adjusted over the years, whilst the Seiko may not have been adjusted at all, and the conditions in which each has been kept over the decades may also have influenced their performance. But I believe there's something more.

When I put any of my Seiko Twin Quartz watches on a Witschi QT-3000 (on the side that takes a rate from a measurement of the oscillator frequency), the displayed rate fluctuates constantly. This is what you'd expect with two oscillators continuously putting out conflicting frequencies. The Longines, however, returns a nice, steady rate, except for periodic fluctuations. To me, this suggests that the approach taken by ETA differed from that taken by Seiko. The Seiko Twin Quartz movements have no inhibition periods. They constantly adjust for temperature changes as the measured difference between oscillator frequencies changes. Service manuals advise that the Twin Quartz watches cannot be timed on a QT-99 using any of the standard 'gate' timings, but have to be timed on an open setting and with the stem pulled out to stop the auxiliary oscillator. I believe ETA's dual oscillator movement has the auxiliary oscillator kick-in only once in each inhibition period. I believe this idea is further supported (beyond the results from the timing machine, that is) by the fact that the battery life of the dual 32 kHz Seikos is three years, while the battery life for the variants wielding both 32 kHz and 40 kHz oscillators shrinks to two years on the same battery. The ETA movement is said to use a 262 kHz oscillator as its auxiliary, and it sports a battery of similar size to that used in the Seikos. Honestly, you don't have to be an electrical engineer to see that the ETA would run out of juice in pretty short order if both oscillators were running all the time.

The effect of using a much higher frequency oscillator would be a more accurate temperature calculation. The effect of switching it on only once per inhibition cycle would be both to conserve batter life but also to reduce the effect of crystal ageing. The ageing of the Seikos' auxiliary oscillators would occur far more quickly than would be the case in ETA's movement, resulting in a speedier decline in the maximum achievable SPY value for the Japanese movements. So, while Seiko's Twin Quartz watches struggle to stay on spec., today, my dual oscillator Longines sits comfortably at the top of my performance chart.

Digital count adjustment

Thought to be the basis for all modern thermocompensated movements from ETA, digital count deduction is based on the cross-referencing of measured temperature against thermal performance data. It is also broadly assumed that all top, modern movements (from any and all manufacturers) use just one crystal oscillator and that that oscillator has a frequency of 32 kHz. It is worth reiterating, however, that, for the most part, we just don't know this for sure.

When I put a DS-2 on a heater and observe the rise and fall of its rate, the thing flat-lines at 50 degrees centigrade (that is to say, the rate ceases to rise and fall and just becomes completely steady), possibly lending weight to the idea commonly mooted in HAQ circles that TC movements may deduct count but not add count. But then there's the DeHavilland watch whose creator told me that count can be both subtracted and added, in his product. I have read, somewhere, that Citizen have claimed not to use TC at all, but I haven't seen anything directly from Citizen in that vein and I think it is simply beyond belief in HAQ circles that a 5 SPY watch could promise such accuracy without employing some method to combat the problem of changing temperatures. We know they once did it with MHz-range oscillators, but we're fairly sure those days are behind us. We're on slightly surer ground with ETA, but even the apparently open Seiko is shrouded in a bit of mystery. Do they use count deduction and is it digital or analogue? Prevailing wisdom says they do use count deduction and that it is 'digital', but bloggers and senior members of Japanese watch fora are somewhat insistent that Seiko use an analogue method (and some even suggest that count deduction might well be a technology that the Swiss have entirely to themselves).

Radio and GPS and other synchronised options

Junghans were the first to come out with a wristwatch that could synchronise its time with the radio signal from an atomic reference clock. Often called 'radio-controlled' watches in the UK, and 'atomic' watches in the US, these watches tend to have no greater inherent accuracy than an ordinary quartz watch. They may boast of 'atomic' level accuracy and not losing a second in ten thousand years, but in reality any of my newer HAQ watches will almost certainly lose less time in a month than an RC watch will lose over the course of a day. The watch may have showed the correct time when it sync'd at 2 a.m., but by tea time you really would have no idea what the precise time was. And no, you can't just be blithely dismissive of the importance of that second. Not when the very boast of the watch is that it has '1 second per 10,000 years' accuracy.

Much the same thing is true of GPS-sync'd watches. Seiko may have brought GPS to the wristwatch, but Citizen seem to be the only ones to have done anything to improve the un-sync'd accuracy of their GPS range of watches, with their F900 holding 5 SPM in the absence of satellite data. Apple may have boasted that their watch is accurate a second in ten thousand years (or whatever it was that they said), but again this relies on the watch getting its time signal from the 'phone which, in turn, gets its time signal from a broadcast atomic reference. Disconnect these devices and their time-keeping falls back to the levels of the earliest quartz watches (or worse).

MorgenWerk have released a series of watches that are GPS-sync'd and also boast self-learning TC to provide an un-sync'd rate of 0.75 SPY, and Hoptroff have an internet-sync'd watch that promises 1 SPY in much the same way, but if you have never heard of these companies then you are not alone. This is not mainstream technology by any stretch of the imagination. Logically, it's the direction in which horology should be moving. Xonix tried a similar approach with watches that could synch via a web app and trim their own rate as necessary, according to accumulated data. Some implementations of the technology were found to work, while others were not. These cheap-and-cheerful watches lacked thermocompensation, but they showed what ought to be possible. Now that we have both Hoptroff's and MorgenWerk's versions of this self-calibrating technology in thermocompensated watches, we are finally starting to see real evolution in precision time-keeping. But let's not lose sight of the fact that these two, small companies do not necessarily mark the beginning of a sea change in the industry. Unless their technologies are taken up by one or more of the big manufacturers, it's hard to say that the world of high accuracy watches has really moved on.


Both Hoptroff's smartwatch and MorgenWerk's GPS watch may struggle to justify their existence as both smartwaches and GPS watches are already widely advertised as being dead-on accurate all the time. Only those who really pay attention will notice that they aren't, and maybe even fewer will really care that much. As long as a connected watch or a GPS watch syncs from time to time, it's probably ok for most users. It's an uncertain time for the horological hopeful. But these self-calibrating, thermocompensated, 1 SPY watches are not the only fledgling technologies hoping to secure footholds in the market. Hoptroff also has atomic watches.

Not 'atomic' like what some people call those radio-sync'd watches, but watches with small atomic clocks inside. In low power mode they can offer accuracy of 1 second per hundred years. In full power mode, that goes up to 1 second per thousand years. The size and cost would no doubt rule out these watches for most consumers, even if they had even heard of their existence. Definitely as accurate as a watch could hope to be, but, as with the other offerings from Hoptroff and Morgenwerk, not game-changers just yet.

And so, here we are. In 45+ years of quartz watches, is this as far as we have come? Thermistors and digital count correction? 5 to 10 seconds per year? We had that in 1978! Are quartz manufacturers now giving up on the pursuit of ever more accurate timepieces and following the path trodden by makers of mechanical watches, refocusing their efforts on complications and design features? Citizen, Seiko and ETA continue to develop and produce new high accuracy quartz movements, but they are all still rigidly spec'd to 5 or 10 SPY. I have the self-learning, thermocompensated watches of Morgenwerk and Hoptroff and I am considering saving up for one of Hoptroff's atomics, too, but these are niche players and, in all honesty, I'm not particularly confident that they will still be around, ten years from now.

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