Wednesday, January 04, 2006

Wristwatch Accuracy and the Penultimate Timekeeper

Watch aficionados - did this happen to you on New Years Eve? Midnight is near, and you set your certified chronometer against your atomic radio-controlled Casio earlier in the day so you'd know WHEN to kiss your date. As the moment gets closer people start counting down - but they are no in synch with your watch. You KNOW your watch is right, so you begin to count down the correct time, trying to get the crowd on your beat. Too late - they're already too loud, and they ring in the New Year a full three seconds early. Peeved, you forget to kiss your date, and another year starts off badly...

Well, it seems people don't care about watch accuracy all that much, even when it counts. Watch collectors are holdouts in this world gone metrologically mad - most collectors have some concept of timekeeping accuracy, and each has their own tolerance for deviance in his or her timepieces. "How accurate should my watch be?" is one of the most common threads on watch collecting bulletin boards, especially among new members.

In an interesting thread on WatchUSeek , a poll was taken asking how accurate members expected their watches to be. It turns out that 70% of respondents felt that COSC standards (+6/-4 sec/day) or a slightly looser +/-10 sec/day was acceptable. A laissez-faire 15% said that +/-30 sec/day was fine, while precisely 4.72% demand atomic clock accuracy.

I fall somewhere in between, finding a 10-20 sec/day deviation in most mechanical watches okay for me. I don't mind resetting my watch every few days. I think many collectors who own several mechanical watches, and who don't keep them constantly wound, will ultimately fall into the easygoing range that I accept. However, in my mind brand new or high dollar watches should produce COSC-like rate results.

Aside from what a collector will accept, what is realistic? Well made mechanicals, using in-house or modified commercial ETA movements, should realistically keep time within COSC standards. However, a buyer should not assume any given accuracy not claimed by the manufacturer; big names do not always ensure that a manufacturer will adhere to the consumer's expectations of accuracy.

Some unmodified ETAs might do as well as a COSC certified watch, and rates for identical models can vary on a watch-by-watch basis. For an ETA or most Seiko mechanical movements, 10-15 sec/day is not unreasonable. In my experience, Miyota (Citizen) mechanical movements are in this range as well, but may vary a bit more on a per watch basis. Timekeeping performance can degenerate over time, and a slow watch is a good sign of a watch that needs service. Performance can also quickly degenerate if the watch is subjected to shock, temperature, or moisture beyond its design limits.

Collectors can find lots of technical information on the ETA SA regarding their movements, but nowhere are any accuracy claims made. The final adjustment and performance of the movement is the province of the watch manufacturer.

Quatz watches are inherently much more accurate than mecanical ones - some collectors like quartz, some don't. The ocillation of the crystal in a quartz watch is many times more regular than any counterpart balance in a mechanical watch; quartz crystals are not subject to positional error due to gravity, and are not subject to rate change due to the winding/unwinding of a spring. They are, however prone to loss of accuracy due to temperature and moisture. Quartz watches are commonly accurate to +/-15 sec/month.

The ultimate timekeeper would be an atomic wristwatch - atomic clocks are so accurate that scientific notation is required to express accuracy. The best a conventional quartz watch can do is link regularly to an atomic clock standard, usually by radio. A quartz watch that loses half a second per day, but re-sets itself to an atomic clock every night, is effectively always on time.

The penultimate timekeeper is the thermocompensated quartz watch. Keeping time within +/-15 seconds a year, without reference to an external standard, these watches are engineering marvels. For the last word on thermocompensation, I would refer the reader to the outstanding article by Bruce Reding at the WUS High-end Quartz Forum.

There are a few ways to improve the accuracy of a watch. As has already been noted, keeping a watch clean and oiled through routine service is a good place to start, but watchmakers and enthusiasts can do more. Adjusting the accuracy of a watch by changing the rate of oscillation of the balance is called regulation. Regulation makes fine adjustments to the rate a watch beats, so that fewer beats are gained or lost per hour in relation to the ideal rate a watch is geared for.

"How accurate should my watch be?" The short answer is 'as accurate as the manufacturer specifies.' Buying a watch and expecting it to perform beyond these claims can lead to heartache. Determine what is comfortable for you, and buy accordingly. Once bought, keep the watch maintained, just as you would your car or any other piece of important machinery. Then, wear and enjoy it!

How does this help us in our New Years Eve scenario? Unless everyone is wearing a radio controlled atomic quartz, or a thermocompensated quartz watch....not at all. Just lighten up and join the countdown with everyone else. Your date will thank you.



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