One of the most common questions regarding automatic watches is the accuracy. It’s a question that I also have for some time and here I’d like to share what I’ve found out about it.
So what is considered a good accuracy for an automatic watch? A commonly acceptable good accuracy for an automatic watch is around +/- 10 seconds per day, although this will vary depending on few factors.
As you will see later on, each watch manufacturers have their own published specification for accuracy depending on the movement which is the range of accuracy that you should expect to get. In addition, there are some usage patterns that can affect the accuracy of our watches.
Automatic Watch Should Be Accurate To The Manufacturers Specification
I’ve arrived at the “good accuracy” value of +/- 10 seconds per day rate based on my own personal experience as well as many other automatic watch users.
In my opinion, the +/-10 seconds per day accuracy limit is a good benchmark for real life use. To put this in perspective, the +/-10 seconds per day corresponds to 0.011% inaccuracy over the span of a day – which is still quite good in my opinion.
This will correspond to about maximum +/-70 seconds per week, which means you will need to adjust your watch every 1 or 2 weeks, depending on how accurate you want it to be to the real time.
Without a doubt, you don’t want to have to set your time again more than once per week – that’s just too cumbersome even though I love to interact with my watches.
While this is just a good guideline, the actual accuracy range depends on the movement itself. Some movement can have small tolerance while others (the Japanese usually) can have a bit of large accuracy tolerance.
Below are the published maximum accuracy of some of the most popular automatic movements out there:
- Seiko 7S26 (inside the SKX ranges of watches): +49/-20 seconds per day
- Seiko 4R36 (inside latest Seiko low-mid range of watches): +45/-35 seconds per day
- Seiko 6R15 (inside Seiko mid-range of watches): +25/-15 seconds per day
- Orient F6922 (inside latest Orient watches e.g Mako/Ray II): +25/-15 seconds per day
- ETA 2824-2 (most commonly used movement in Swiss low-mid range of watches): +/-12 seconds per day
- Sellita SW-200 (ETA 2824-2 doppelganger and used in Swiss low-mid range): +/-12 seconds per day
As you can see from above, the published accuracy range for most movements non-chronometer is usually very large. This is because most of these movements are mass market movements and the manufacturers would like to play it safe with their published accuracy.
But real life accuracy shows that most of these modern movements can perform way better. In my own watches, the out of box accuracy is lesser than +/- 10 seconds per day.
Why Are There Accuracy Differences Between Movements?
The Japanese (Seiko and Orient) typically have upwards of 20 seconds per day accuracy limit while the Swiss (ETA and Sellita) is much lower at just +/- 12 seconds per day.
One of the biggest reasons for this is in the beat rate of the watch movements.
The Japanese movements have a low beat rate of 6 beats per second (21,600 vibrations per hour) while the Swiss movements (ETA 2824 and SW-200) have a higher beat rate at 8 beats per second (28,800 vibrations per hour).
With a higher beat rate, the movement will have a higher accuracy tolerance as the high beat rate will be able to iron out any discrepancies in the timekeeping from the balance wheel better.
Another example is in the Seiko 9S85 hi-beat movement with 10 beats per second. This upper range of movement has a great accuracy of just +5/-3 seconds per day, a great testament to how beat rate affects accuracy.
In the past, watchmakers were in the race to produce the highest beat rate movements in order to improve accuracy (some even up to 16 beats per second). But such high beat rate will take a huge amount of power reserve because of the increases times the parts are moving, so much so it’s only reserved for some of the more expensive watches.
Material quality and movement design also play a huge part in terms of accuracy.
For example, a typical Swiss ETA 2824-2 comes in 4 variations (standard, elabore/special, top/premium & chronometer – in order of higher accuracy and price). The higher end variations comes with better balance wheel material to give a higher accuracy.
In addition to this, some watches also are adjusted in the factory before being shipped. This is usually applicable to the COSC chronometer watches which need to be tested by the COSC institute with a limit of average rate of -4/+6 seconds per day.
As such, the chronometer watches will be adjusted by their watchmakers before being sent to be tested. Once it passed, a certificate will be issued with the watch to its prospective owner. As far as accuracy in automatic watches goes, these chronometers sits at the top of the pyramid.
Adjustment or lack of adjustment is also one of the reasons why most Japanese movements have such huge range of published accuracy. Adjusting each watches prior to shipment takes a lot of time and effort, and is not feasible for Seiko and Orient to do as they placed affordability as their key value proposition.
Why Does My Automatic Watch Run Fast/Slow? Here Are Some Usage Patterns That Affect Accuracy
Do you have a problem with automatic watch run fast or slow? Automatic watch run fast or slow can be attributed to many factors such as temperature, magnetism, lack of service or even damage to the movement.
Automatic watch is made of more than a hundred of small minute parts which are moving concurrently to tell time. With such a complicated and delicate device, any factor that can affect its smooth operation will be affecting its accuracy.
For example, as the watch parts are made of metal, temperature swings will play a huge role in its operation. Metal will expand at high temperature (anything above 40 degrees Celsius, such as in Sahara desert) and will contract at low temperatures.
It’s quite typical for an automatic watch to lose time at high temperatures and gain time at low temperatures due to its metallurgical properties.
Magnetism will also cause inaccuracies. This is why you should not place your automatic watch near to a strong magnet or any electronic objects (beware of your computer and smartphone). The strong magnets can affect the metal parts and magnetize it, causing disruption in accuracy.
Lack of service is also another culprit. For Swiss watches, consider sending it to be serviced every 3-5 years to keep it running optimally. While Japanese movements are generally more robust and require longer service time, it will also be subjected to reduced accuracy if not being serviced for a long period of time.
One of the things that you can do to get a better accuracy is to keep track of the position of your watch. Automatic watch is greatly affected by gravity and the placement of it (either dial up, down, worn in right or left hand) will have effect on its accuracy.
What you can do is to see how the accuracy changes depending on position of your watch at rest (do you put the dial up or down?). Then try to change it and see how it goes. As the accuracy of the watch is an average for the whole day, you can rest your watch so that it will cancel out the loss/gain time when you wear it.
Last but not least, any damage to the movement due to sports or sudden impact can impact its accuracy.
What Should You Do If Your Watch Accuracy Is Faster/Slower Than The Acceptable Limit?
One of the first things that you can do to rectify your watch’s accuracy is to manual wind it. It’s important to know that the accuracy of the watch is the best when it has high energy supply from its mainspring. From my own experience, manual winding my watches will give an immediate improvement in accuracy which is why I’m recommending this first.
With a high power reserve, the mainspring is tight and this will translate to a high driving force along the gears and movement. And one of the best ways to top up your power reserve to full is by manually winding it.
But if you don’t notice any improvement, then you can bring it to a watchmaker to have a look. If the watch is still not due for service and there is no sign of damage whatsoever, then you can ask to have your watch adjusted to your desired accuracy.
One thing that you should mention to your watchmaker is how you usually wear your watch and store it e.g on right hand, dial up on the desk at night, for how many days you usually wear the watch. This will enable the watchmaker to adjust the watch specifically for your needs which will give a much higher accuracy over time.
Do all automatic watches lose or gain time? All automatic watches gain or lose time over their entire life due to the inaccuracies in-built within the mechanical movement.
How to check watch accuracy? Watch accuracy can be checked either by manually comparing the watch time with atomic time, using an app or using a timegrapher. I’ve also written an entire article regarding this topic if you want to know more about it.
I hope this article about what is considered a good accuracy for an automatic watch will be beneficial to you. Do let me know if you have any other questions regarding this topic.