Dispelling myths and misconceptions about how well a good watch tells time
An expensive watch is more accurate, right?
"Excellence is achievable, perfection is much more elusive."
(origin unknown).
If this is your first time buying an expensive wristwatch, there is one very important fact you need to know in advance. A $25 Timex or Casio digital watch will keep time just as well as, and possibly better than, a $20,000 solid gold mechanical Omega, Rolex, or other very fine watch.
If that last statement surprised you, read the rest of this section carefully.
All watches tend to gain or lose a few seconds over a period of time. These are small mechanical or electro-mechanical devices that are counting out 86,400 seconds per day. Even if a watch is 99.9% accurate, it will still be off by a minute and a half in only 24 hours! So even a mediocre wristwatch has to be well over 99.9% accurate to even begin to be useful on an ongoing basis.
So, what is a reasonable expectation of accuracy from a wristwatch?
Vintage mechanical watch
in good repair +/-60 +/-15 +/-5 99.9826%
Modern mechanical watch
non-certified +/-10 +/-5 +/-2 99.9942%
Modern mechanical watch
chronometer certified +6/-4 +/-3 +/-1 99.9977%
Modern quartz watch
non-certified (normal) +/-2 +/-1 +/-0.1 99.9998%
Modern quartz watch
chronometer certified (rare) +/-0.02 +/-0.02 +/-0.0 99.9999%
So what makes a mechanical watch a "Chronometer" or "Certified Chronometer?"
Fine watchmakers often have their mechanical watch movements individually certified by the Contrôle Officiel Suisse des Chronomètres. COSC is the official Swiss institute responsible for certification of wristwatch movements. Only watch movements certified with a COSC 'bulletin de marche' (certificate of watch performance) are allowed to bear the internationally protected label "Official Swiss Chronometer" or even use the word "Chronometer" anywhere on the product, packaging or advertising.
The standard used by COSC is to test the accuracy of a mechanical wristwatch movement--before it is assembled into a watch--for consistent accuracy under a range of position and temperatures. COSC actually peforms seven tests as part of the certification. But the most commonly mentioned is the "mean daily rate" test for which a standard men's watch size mechanical movement, the watch must maintain an accuracy within -4 to +6 seconds of variation per day (that's +99.994% accuracy!).
The other six less mentioned measurements are: mean variation in rate, greatest variation in rate, horizontal and vertical difference, greatest deviation in rates, rate variation due to temperature and resumption of rate. Overall, these tests measure not only the overall daily accuracy but also the consistency under various normal ranges of conditions.
It is also important to note that a "COSC certified chronometer" is not the Holy Grail of watchmaking. With the high quality of modern manufacturing, this test is nowhere near as important as it was several decades ago. Most decent modern watches, when adequately adjusted, should be able to match the performance specified by COSC.
A chronometer certificate is not a guarantee of future accuracy. Watch movements that have been certified can get out of adjustment and perform poorly. Movements that were not certified may still exceed the COSC standards--the manufacturer may simply have simply chosen to bypass the expense of the certification process.
Are quartz watches always more accurate than mechanical ones?
Typically they are, but not always. Accuracy and precision are not exactly the same thing.
It is important to remember that even when a mechanical watch is allowed to vary +6/-4 seconds per day, that does not mean it will consistently vary by that high an amount each day. Mechanical movements--except the very rare 'turbillon' movements that correct for it--are noticably affected by the gravitational pull of the Earth. It only takes a performance distortion of 1/1000th of a percent for a watch movement to be one second less accurate in a day. This causes the performance of mechanical movements to be somewhat different from day to day when not stored in a fixed position. The good news is that the actual variations of a mechanical watch will often cancel each other out. This means a mechanical watch will tend to be more accurate over a longer period than the single-day COSC measurement may imply.
The day-to-day performance of quartz is much more consistent than mechanical under identical conditions. Quartz performance is affected mainly by temperature changes and weakened batteries. So a quartz watch that you measured to gains 0.5 second yesterday will be consistently increasingly off correct time by about that amount. You can be pretty certain that in 60 days, it will be about 30 seconds off. At the end of a year, it would be likely be over 180 seconds off.
Compare that to a mechanical watch that you measured to gain 2 seconds yesterday. It would seem that our example quartz watch is 4 times more accurate than this. But while the daily measured daily variations seem much higher, they are not likely to be as consistent, so will have a dampening effect. You cannot accurately predict that this mechanical would therefore be off by 120 seconds at the end of the same 60 days. It might be right on time, or it may be 200 seconds off. That broader range of variations allows most mechanical watches to stay closer to correct time than the daily variation rate implies. Over a year, some mechanicals can on average stay closer to correct time without having to be reset than a quartz watch might.
Why would I want a mechanical/automatic watch when quartz is more accurate?
Simple. Quartz is clearly better on accuracy. But there are many other advantages and pleasures from wristwatch ownership beyond just measures of precision levels that are beyond the notice of many people.
Frankly, quartz watches and many other technologies don't really do anything significant to better people's lives. People with quartz watches are no more reliably on time than people with mechanical ones. People driving cars with manual or automatic transmissions still get where they are going equally well. People still enjoy music about as much as they used to, even though CDs play it more clearly that tape or LPs did. You are not likely to have any smarter thoughts simply because you wrote them down with a computer than with an ink pen. And you can certainly do a lap around the lake faster in a speedboat than in a rowboat, but what have you really accomplished?
The newer technologies often gain a level of efficiency that makes them... uninteresting. In many cases, the older ways and technologies were more than sufficient, and it is their minor failings that give variety and character to doing things that way. With the older ways, you usually have to be more aware of details, understand more of what you are doing, and take more time being involved in the process. That greater interaction makes the process more personal and enjoyable for some people.
With the newer ways, you can be pretty assured your quartz watch is on the right time, your car's automatic transmission won't miss downshift on the way home, your CD will play exactly the same as it did yesterday, your computer will catch and correct your typos and misspellings, your video game won't stop in the middle because of rain or a player injured in a tackle, and you certainly won't be bothered seeing much of the detail and wildlife on the lake at high speed from your motorboat. How boring.
Mechanical watch enthusiasts often compare the movements, the finishing, the level of adjustment, types of certifications, performance under different circumstances and other esoteric measures of mechanical timepieces.
Quartz watch enthusiasts compare... mostly accuracy measures.
So if efficiency is your main desire, then quartz is for you. If you are tired of efficiency and want something interesting instead, try a mechanical watch.
I am worried after reading on the Internet about some people having a problem with the watch I'm thinking about buying.
Virtually none of any of the 'problems' you might hear about are more than isolated cases. Expensive watches are not different from any other elaborate mechanical item, whether it is Rolex, Omega, BMW, Mercedes, or other such items that are simultaneously high-end and large production volume products. Despite superior quality control procedures, all are subject to minor manufacturing inconsistencies and technical glitches. It is virtually impossible to find any luxury brand of technical product that at least a few people have not had a problem with.
In addition, many first-time owners of luxury and mechanical watches have misunderstandings and unreasonable expectations of the operation, accuracy, durability and limits of these fine timepieces. So often, complaints or criticisms come from concerns not actually related to any real defect or problem with the watch itself.
To give some perspective to the issue, consider the largest of the luxury watch manufacturers, Rolex, who manufactures over 1,000,000 watches a year. Even if they have an astronomically high 99.995% perfection rate (they do not publish their actual rate, so this number is purely an example of an extremely high perfection rate), that means that over the past ten years, 50,000 watches may have been sold with imperfections that might need to be addressed.