back to top

Accuracy: Understanding What To Expect From Modern Mechanical Watches

Accuracy: Understanding What To Expect From Modern Mechanical Watches Featured Articles

Article written by Ashton Tracy

Precision. It’s a word synonymous with the luxury watch industry. The collectors and enthusiasts of today demand the highest performance from their watches, and rightly so given the top price tags of luxury pieces. The measurement generally relied upon to gauge the worthiness of a mechanical watch is timekeeping accuracy. Today, watch companies are advertising an accuracy that is greater than ever before, but what does this mean for the average consumer? How can these numbers be interpreted to clearly understand what level of performance to expect from your watch?

Accuracy: Understanding What To Expect From Modern Mechanical Watches Featured Articles

Changing Accuracy

Since the age of church turret clocks, which were able to tell time to the nearest hour, watchmakers have sought greater precision from mechanical time-keepers. Over the next few hundred years, clocks became more precise. Marine chronometers were developed and displayed greater timekeeping accuracy at sea. Portable pocket watches went from strength to strength.

In the late 1800s, the wristwatch entered the scene and changed the landscape of mechanical watchmaking forever, becoming more and more commonplace as the years went on. Eventually, these were the only watches the public wanted. Here was a revolutionary product that meant time was always with you, and a casual glance at the wrist was all that was required. They were small, portable, and practical compared to pocket watches, which were bulky and cumbersome.

While the wristwatch was undoubtedly revolutionary, it did bring with it a whole new set of problems. This tiny horological machine was now portable and required the ability to be thrust into various positions on an almost constant basis.


Accuracy: Understanding What To Expect From Modern Mechanical Watches Featured Articles

Over the next hundred years, watchmakers developed new techniques and improved on existing designs to obtain greater accuracy from mechanical watches and overcome the hurdles of gravity. As a result of that, wristwatches today are the most accurate they have ever been and set to become more accurate in the future as a result of new manufacturing techniques and concepts.

In modern times, chronometer certificates issued by C.O.S.C. have been the industry standard for timekeeping. The chronometer certification requires a watch to keep an average daily rate between the parameters of +6 – 4 seconds per day, as measured over the first ten days of testing. There are also thermal variations taken into account, but we won’t get into that here.

Accuracy: Understanding What To Expect From Modern Mechanical Watches Featured Articles

In the last few years, however, companies are refusing to rest on their laurels and are pushing the timekeeping boundaries further. Chronometer certification is still a reliable benchmark for accuracy today. But watch companies have put forth new and improved testing and timekeeping requirements.

Patek Philippe has created its seal, which requires calibers over 20mm to be accurate to -3 +2 seconds over 24 hours. Omega has employed the M.E.T.A.S. certification, which states that the watch must accurately record time between 0 and + 5 seconds per day. The Geneva Seal have updated their timekeeping requirements to ensure that a watch does not exceed 1-minute variation over 7 days.

With new certifications and testing requirements being rolled out across the industry, what do the figures we read about in these certifications mean in a real world scenario on your wrist?

Accuracy: Understanding What To Expect From Modern Mechanical Watches Featured Articles

Run The Numbers

With watch timing machines being manufactured relatively inexpensively these days and watch-timing apps available on all smartphones, collectors are keenly interested in testing the performance of their watches, and so they should be. As brands claim greater accuracy than ever before, it’s essential to hold them to account and make sure the stated numbers are a reality. But when reading these figures, we need to know what we are reading.

Accuracy: Understanding What To Expect From Modern Mechanical Watches Featured Articles

For this article, we shall look at the stringent new Rolex requirements.

For a Rolex watch to meet its requirements, it needs to keep time within plus 2 seconds to minus 2 seconds per day. That means it can only gain a maximum of 2 seconds or lose a maximum of 2 seconds in 24 hours.

There are two horizontal positions and three vertical, or hanging, positions in which the movements are tested, giving a total of five overall positions. These positions represent the dial facing upwards and then downwards and the vertical positions of 3 o’clock (pointed upwards), 6 o’clock (pointed upwards) and 9 o’clock (pointed upwards). These are the most common positions for a watch to be in. Examples would be a hand pointed to the floor, a hand resting on a table, and a hand pointed toward the sky.

Accuracy: Understanding What To Expect From Modern Mechanical Watches Featured Articles

The + 2 – 2 requirements are an average taken over all positions of testing. The watch is adjusted to a specific time, say plus-2 seconds per day as calculated by a watch-timing machine. (The machine uses the sounds that the escapement makes to gauge how the watch is performing and converts that to numerical data.)

The watch is then tested in the various positions we discussed. The following chart explains a typical readout from a watch-timing machine.

Position Of Watch Seconds Per Day
Dial Up +2
Dial Down -1
6 o’clock +3
9 o’clock -3
3 o’clock +5

At first glance, it may look as if the watch is out of tolerance for Rolex timekeeping requirements as +5 seconds and -3 seconds are well out of the +2 -2 range. I have read many forum posts from people checking the timekeeping of their watches and being concerned that they are not within the brand’s specifications. However, this watch is actually in spec for Rolex.

The five figures need to be added together and then divided by the number of positions tested in to reach the +2 – 2 requirement. Add the positive values together and subtract the negative, and the result is positive 6. Then, we divide six by five (the number of positions), and we get the number 1.2.

Accuracy: Understanding What To Expect From Modern Mechanical Watches Featured Articles

The watch in question keeps time to +1.2 seconds per day, which is within the Rolex requirements, even though each position doesn’t meet the +2 – 2 seconds outlined. From these figures, we understand that a more significant gain in some positions and a loss in others could still be acceptable. Other requirements come into play, such as maximum allowable differences, temperature, testing times, and the amplitude at the wind, Still, the figures discussed give all the information that is needed to understand the testing requirements accurately.

Accuracy: Understanding What To Expect From Modern Mechanical Watches Featured Articles


It is evident from the information discussed why brands felt the need to update the timekeeping requirements of their products and make their specifications higher than that of C.O.S.C. While C.O.S.C. still tests Rolex and other movements, it’s good to see brands keeping up with the consumers of today who require more from their watches.

We live in an enlightened age where technology is cheap and information abounds. Checking the accuracy of mechanical watches and knowing the standards are tasks that can both be completed from the comfort of our own home with a smartphone, but making sense of that information can be confusing. Having the knowledge to make sense of the results you see and comparing them to the stated accuracy helps to avoid the frustrations of the at-home testing equipment that may lead you to believe your watch is not performing well when it actually is.




Disqus Debug thread_id: 7763511290

  • Agnar Sidhu

    Thank you for the great read! Timekeeping was /is the watches purpose, and it only makes sense that accuracy is a key figure for a watch.

  • Agnar Sidhu

    Anyone who has an app they’d recommend?

    • Lellobservi

      Hairspring is a cool app, that I have used for some years now.

      • Agnar Sidhu

        Thanks, I’ll check it out:)

    • Berndt Norten

      There’s an app that might recommend one ?

    • You can also try (for Android) WildSpectra Mobile Lite (one of the best), Clock Tuner, or TICKOPRINT
      And (for IOs) Watch Tuner Timegrapher (not free).
      Well…at the end, however, I decided to buy a timegrapher.

      • Agnar Sidhu

        Thanks Kermit! I went for a free app to start with and downloaded the Toolwatch for iOS. Do let’s see if it can tell me something new:)

  • cronobses

    That’a subject I’m interested in. I even created a account to place my first comment on ABTW. IMHO, the most impressive and conclusive testing is done by Glashutte Original for their Senator Line, all six positions and after purchase you get full recordings over 24h, not just the difference t=0h / t=24h. Amplitude and rate stability DURING the 24h are what separates a good from mediocre chronometer.

    If my watch would show a +5s/d at the 9h and -3s/d at the 3h, i.e. a 8s/d delta in the 180° differing positions, I would get it serviced if it is a modern chronometer. There’s an imbalance in the balance wheel.

    In 2019, any rate recordings should be given with an accuracy of 0.1s/d. In your photo I see a rather dated acoustic measuremet device probably not yielding the most precise measurements, but ok for a quick after sales check. Maybe a thought for future articles: Modern chronometric measurment systems. There’s plenty of work needed, think of silicon parts in escapements (less mechanical noise, rendering acoustic detection difficult), other escapements with different noise patterns than a swiss anchor escapement, extremely high frequencies (think of the 50Hz oscillators). You may want to check out modern devices of the likes of the videobalisometre, chronotracker, femto wtm, etc. on which the watch manufacturers rely on in their laboratories and development departments. A visit to the Geneva fair called EPHJ might be advised? It’s where the subcontractors, suppliers, service companies show their offerings (entry is free, but no fancy watches to admire).

    PS: I am not linked in any way to Glashutte Original.

  • Han Cnx

    Excellent article, and I for one am extremely interested in the highest possible accuracy for mechanical watches. I see relatively a lot of opinions out there that go something like ‘if you care about accuracy, buy a G-Shock/quartz/smartphone/etc.”. But I think that is missing the point. The goal of any timepiece MUST be to achieve the greatest possible accuracy (and reliability, ruggedness, etc.) Yes that will always be less than a quartz watch of comparable quality, but I think it’s possible to achieve the same accuracy or better than more basic and mid-range quartz watches. A truly stunning achievement using mechanical springs and wheels, and something well worth owning!

    • Poul Winther Knudsen

      If you’re honest with yourself, you simply don’t buy mechanical watches because of their accuracy.

  • SuperStrapper

    Great article, really. Fun reading, but that is really the extent of my interest in hyper accuracy. It’s all just such hyperbole to me, people don’t actually need this level of accuracy; it’s all bragging rights and conversation fodder. Which is fine, i don’t suggest that it shouldnt be strived for, but I just need my watch to be “accurate”. I own about 50 of them and i don’t believe in winders, so I’m constantly resetting them anyway. If I had to choose a watch that had hacking seconds and a 20 second a day accuracy rating or a watch with no hacking seconds that was truly accurate to within 1 second a day, aesthetics aside i take the hacking watch every time.
    I adore mechanical watches and always have, but my collection is also rich in digital and UHF pieces. I have all the accuracy i need.

  • Thank you for this article: very interesting reading.
    Now, I have a question: how about the precision standard and the accuracy range of this PERLATIVE CERONOMETER? 😉

    • spice


  • JK

    What I miss here the human factor. The article about accuracy can speak about the mechanical deviation, not how accurate the time what is shown. When the owner push back the crown meanwhile listening/watching to an atomic clock time source, there should be done two things:
    1) need to be able to catch the second hand. if it isn’t success, you got immediately ~1s deviance. then you put one day to 3, the other day to 9 the watch to balance the deviation, but it still showing the wrong time, as it was set wrongly

    2) need to be able to push back crown without turning it, when you turn the crown during push back, you got ~1min deviance. could be a watch mechanically accurate of you are not able to set the proper time.

    I like watches which not just hacks, but sets the second hand to zero position to aid correct time set.

    Back to what accuracy needed, let say your Rolex got an average 1s daily, let say it is 30s monthly, let say it is 6mins yearly. When do you adjust your watch? You need to adjust for time zone changes 2 times/year, which means 3mins/half year. Does it matter? Some people even set the watch ahead just not to be late. If it is not Rolex, but another watch with daily +5s, it comes to monthly 2,5mins, half year 15mins, which maybe over than tolerated.

  • ray h.

    I see sincere people posting about how accurate their watch is,from rolex to invectia,the invecta knock off of the submariner to be exact and it seems at every price point it’s about good regulation from the start and then keeping the watch wound. Sad that invecta can regulate a watch and seiko has no such care. QC from Seiko it pitiful and I own 2 of them. I guess if you by the more expensive ones as Gs or some steps below that maybe they do better but not on the everyday watches.

    • tellucas

      I have there Seiko 5 with an autowind only movement and it looses a lot of time until it fully wound which is two days of continuous wear then it runs average.

  • Agnar Sidhu

    Thanks Frank, I’ll check it out:)

  • Drop files here or
    Accepted file types: jpg, png.