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Seamanship & Navigation Forum devoted to seamanship and navigation topics, including paper and electronic charting tools.

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Old 12-12-2010
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A Rolex, like every "superb mechanical certified chromometer", is only certified accurate within two minutes a month.

A cheap quartz watch typically is within 10 seconds a month. Any of them.

A really good quartz watch, an adjustable one, can do about 15 seconds per year.

But any mechanical watch will need to be adjusted for the user's wear habits, which need to be consistent if the watch is expected to be consistent. The watch position (inside or outside the wrist) can change the rate by more than one minute per month. The position (12 up, stem up, etc) that a watch is left in overnight, if you don't wear it, can change the rate AND that's also a good way to modify the rate if you need to.

And then again, Rolex seems to say their watches need an annual cleaning and lube in order to run reliably.

I know the rate of my watches, more or less. One loses 15 seconds per month, which I call 1 second per two days, while the battery is good but that changes after a year. Another loses a bit more, but the battery is good twice as long. The Casio embarasses them both. But just for ****s and giggles I prefer to use GPS-time (which can need correction too, partly because it needs to be on for about 20 minutes in order to make sure it gets one full correction message from the network) with the sextant. Knowing I'm getting a time signal from a dozen or more atomic clocks...maybe $20 million dollars worth of CLOCKS giving me that time signal...How can you not laugh?

I'll hack a cheap stopwatch "on the hour" with the time, and then squeeze the "lap" button when taking a sight. That gives me a time which is pretty much identical to the moment of the sight, rather than trying to correct a bit more more for "look here, now look there", for what little extra precision that's worth.

Doesn't really matter what you use as long as it is a consistent timekeeper, worn or kept consistently, with the rate of gain/loss noted and known.
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Old 12-12-2010
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Originally Posted by hellosailor View Post
A Rolex, like every "superb mechanical certified chromometer", is only certified accurate within two minutes a month.
A mechanical watch is not as accurate as a quartz watch.
They are nerveless superb pieces of engineering, which are not dependant on battery power, are immune from electronic surges, and generally accurate enough,
The "certified chronometer" standard is exceeded easily by most mechanical watches. This is a worse case standard.
If you want a watch that survive anything a mechanical watch is a good choice. If you want a watch with a best accuracy a quartz watch will be better.
Cheap quartz watches are often as good as more expensive models. The dearer models generally house the same movement in a more expensive case
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Old 12-13-2010
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Originally Posted by paulk View Post
It is intriguing that the further some people are out to sea, the more accurate they want their timing to be. Shouldn't you be able to find local noon anywhere pretty accurately with a sextant? If you're 500 miles from shore, what difference does 20 or 50 miles make? Accuracy is most needed when you're closer to the rocks - but you should be able to see the shore if you're that close. If it's too foggy, you're not going to be sighting much through a sextant either. Slocum used a hand-wound alarm clock, and probably erred on the side of caution.
Local time for latitude but for longtitude you need GMT/UT-you can do it through a complicated calculation using positions of the planets and stars as was used on Cookes first voyage but the accurate mechanical marine chronometer of which Cooke took one of the first on his second voyage still remains the best mechanical self contained means of getting UT/GMT.
It was often the case pre marine chronometers that European explorers would find an island particularly in the Pacific and then loose it for a century or so!
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Old 12-13-2010
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"A mechanical watch is not as accurate as a quartz watch."
Generally so, as I noted. However, most quartz watches are UNADJUSTABLE and you take what you get. The better quartz watches, like the fine mecahnical ones, are adjustable and if you are brave and gentle, you can actually adjust the rate of your own watch. Safely.
Many Accutron owners have been able to get their watches running with an accuracy of 15 seconds per month--way better than the original two minutes the watches were built for. The Accutron is a bas, ergh, hybrid design, it is actually a high caliber MECHANICAL watch that simply uses a very crude electronic circuit as the timing base that the conventional movement depends on. And some companies (i.e. Omega) sold the same movements as both chronometer certified, and unadjusted. No one will say if the components are the same quality and lack only the adjusting. "Chronometer" status just means some Swiss Elf spent two weeks rotating the watch through all positions and tickling the settings until it was running at a proper speed.
If you own the same watch for ten years, and just open it to refine the speed twice a year, it gets to be a well regulated watch and keeps good time, if it was a good watch to start with.
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Old 12-13-2010
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Are modern watches really that inaccurate?

I posted on a similar thread that my watch (Seiko analogue quartz) went in for replacement batteries and the consequential re-water-proofing and when I got it back it had been set 4 seconds fast. It is now, some 9 months later, still 4 seconds fast when checked against the GMT beeps on the radio.

By the sounds of other posts here, I'm very lucky - I never even think about setting my watch.

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