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A typical automatic watch is accurate to within a few seconds to under a minute per day, depending on its grade. A COSC-certified chronometer must average -4 to +6 seconds per day in testing. Seiko lists its higher-grade 6R20 at -15 to +25 seconds per day, and retailer spec sheets list the budget 4R36 at +45 to -35. By comparison, a basic quartz watch is rated in seconds per month.
So if your automatic drifts 10 or 20 seconds a day, it is probably working as designed. The useful question is whether it stays inside its own published range. Here is what the numbers mean and how to check your watch.
Published accuracy ranges, from budget to chronometer
| Movement or standard | Type | Published daily rate | Source | Amazon |
|---|---|---|---|---|
| Seiko 4R36 (Seiko 5 Sports, Prospex SRPE93) | Budget automatic | +45 to -35 s/day | Retailer spec sheets | See options |
| Seiko 6R20 | Mid-grade automatic, 28,800 beats/hour | -15 to +25 s/day | Seiko | |
| COSC chronometer | Certified mechanical | -4 to +6 s/day average | COSC | |
| Many Seiko quartz calibers | Quartz (for comparison) | ±15 s/month | Seiko | |
| Grand Seiko 9F | High-end quartz (for comparison) | ±10 s/year | Grand Seiko |
Two things stand out. First, the published tolerance for an inexpensive automatic is wide, because the maker is promising a range every watch will meet across positions and conditions, not how a typical watch runs. Many run well inside it. Second, even a chronometer drifts more in a day than a good quartz watch drifts in a week. Our automatic vs quartz comparison covers that trade-off.
What a COSC chronometer is
COSC, the Swiss chronometer testing office, certifies movements that pass its tests. For mechanical movements, COSC says the watch must maintain an average daily rate between -4 and +6 seconds per day over a testing period of 15 days. Movements are tested in five positions (6 o'clock, 3 o'clock, 9 o'clock, dial up and dial down), changing daily, and at three temperatures: 8°C, 23°C and 38°C (about 46°F, 73°F and 100°F). COSC's own overview says testing runs 12 to 20 days depending on the movement type.
That makes "chronometer" a meaningful word on a dial: it tells you the movement passed an independent test, not just a maker's internal one. Some brands also set their own, stricter in-house standards on top of COSC.
Why automatic watches are not perfectly accurate
A mechanical watch keeps time with a balance wheel swinging back and forth on a hairspring, powered by a mainspring. Anything that changes the balance's swing changes the rate. Seiko puts it plainly: the accuracy of a mechanical watch varies slightly each day, depending on how much the spring is wound, the movements of your arm, temperature and the position of the watch.
State of wind
A fully wound mainspring delivers more consistent power than one near the end of its reserve. Many watches run differently in the last hours before they stop.
Position
Gravity pulls on the balance differently when the watch is dial up, dial down or crown up. That is why COSC tests in five positions, and why your watch may gain overnight on the nightstand and lose on the wrist, or the reverse.
Temperature
Metal parts expand and contract with temperature, and lubricants thicken in the cold. Modern hairspring alloys reduce the effect, but it does not vanish.
Magnetism
When a hairspring is magnetized, its coils can stick together and the watch suddenly runs fast, often by minutes a day. If your watch jumps from a few seconds to a large gain, magnetism is the first suspect; see how to demagnetize a watch.
Age and service
As oils age, friction rises and the balance swings less freely. A watch that has drifted steadily worse over the years probably needs service. Our how often to service an automatic watch guide covers intervals by brand.
How to measure your watch's accuracy
You do not need special equipment. Measure over several days, not a few hours.
- Wind or wear the watch fully so it starts with a good state of wind.
- Set it precisely to a reliable time source, such as your phone's clock, at the top of a minute. Hacking movements, which stop the seconds hand when you pull the crown, make this easy.
- Wear it normally for 3 to 7 days.
- Check it at the same time each day against the same reference, and write down the difference.
- Divide the total gain or loss by the number of days. That is your average daily rate.
- Compare it with the published range for your movement.
Watch-accuracy apps on your phone can speed this up by logging photos of the dial against network time. For an instant reading in several positions, a timegrapher listens to the ticks and calculates the rate; our timegrapher guide explains how to read one.
| Your result | What it means | What to do |
|---|---|---|
| Inside the published range | Normal | Nothing; enjoy it |
| Slightly outside, consistently | Out of regulation | Ask a watchmaker to regulate it |
| Suddenly gaining minutes per day | Probably magnetized | Demagnetize, then re-measure |
| Erratic, and worse when nearly unwound | Low power or tired movement | Wind fully; consider service |
| Stops overnight | Reserve too short for your routine | Wear it more, wind it or use a winder |
How to get better accuracy from an automatic
- Use position at night. Find which resting position makes your watch run slow and which makes it run fast, then pick the one that offsets the day's error. Crown up, crown down and dial up are the usual choices.
- Keep it wound. Seiko notes that the amount of wind affects accuracy, so a watch kept near full wind behaves more consistently. A winder set to your movement's published settings does this for watches you do not wear daily.
- Keep it away from magnets. Speakers, laptop lids, tablet covers and bag clasps are common culprits.
- Have it regulated. A watchmaker can adjust the rate, often quickly, and many budget movements run far tighter than their rating afterward.
- Service it on schedule. Fresh oil keeps the balance swinging freely.
If your watch is already running fast or slow and you want the fixes in detail, read automatic watch running fast (or losing time).
Common mistakes
- Judging accuracy over a few hours. Measure over days.
- Comparing a budget automatic with quartz. They are rated in different units.
- Panicking at 10 or 15 seconds a day. For most automatics, that is within spec.
- Ignoring a sudden change. A jump in rate usually has a cause, often magnetism.
- Expecting a winder to fix a fault. It keeps a healthy watch consistent; it does not regulate it.
FAQ
How many seconds a day is normal for an automatic watch?
It depends on the grade. A COSC-certified chronometer must average -4 to +6 seconds per day in testing. Seiko lists its 6R20 at -15 to +25 seconds per day, and retailer spec sheets list the budget 4R36 at +45 to -35. Anything inside your movement's published range is normal.
Are automatic watches less accurate than quartz?
Yes, by a wide margin. Mechanical watches are rated in seconds per day, while Seiko rates many of its quartz calibers at plus or minus 15 seconds per month and Grand Seiko's 9F quartz at plus or minus 10 seconds per year.
Why does my automatic watch gain time some days and lose it on others?
Because a mechanical watch's rate shifts with conditions. Seiko says accuracy varies with how much the mainspring is wound, the movements of your arm, temperature and the position of the watch. A daily rate that moves around within the spec is normal.
Can an automatic watch be made more accurate?
Yes. A watchmaker can regulate it, usually in minutes, and many run well inside their rating afterward. You can also use position at night: a watch that runs fast in one position and slow in another can be rested in the position that offsets the day's error.
Does a watch winder make an automatic more accurate?
It can make it more consistent. Seiko notes that accuracy depends partly on how much the spring is wound, and a winder keeps the mainspring in a steadier state of wind. It will not fix a watch that is out of regulation, magnetized or due for service.
For accurate everyday automatics to start with, see our Seiko automatic watches guide.