'Accurate to within one second in a million years...'
Discussion
I keep seeing these adverts for 'radio controlled' clocks and watches. But there is something that I dont understand. If it is indeed 'accurate to within one second in a million years', then why does it need to get a radio update to stay accurate? and if it gets a constant radio update and is always adjusting itself, then it doesnt need to be accurate at all, any cheap timekeeping mechanism will do, and if it is constantly updating to stay accurate, then how can it lose a second? even if it is in a million years. If it is 'updating' then it will be correct all the time.
I bet Dr Goodfellow would know the answer.
I bet Dr Goodfellow would know the answer.
dilbert said:
I'd have thought that it's as accurate as any other quartz watch. Then on top of that you have a periodic update, which keeps it syncd up with an atomic reference somewhere.
Integral linearity is high, but peak differential linearity is nowhere near as good. In precision terms this is the the signature of most digital devices.
Quoting myself, here's a bunch of stuff about INL,DNL and monotonicity.
Stuff
>> Edited by dilbert on Saturday 12th November 19:38
They are good for resetting themselves when the power goes off during the night, you have a marker from which you can set all the other clocks/videos/microwaves etc that stopped!
They also automatically adjust when clocks go forward or back, so at least, again when you surface in the morning, you have one clock that's showing to 'correct' time.
They also automatically adjust when clocks go forward or back, so at least, again when you surface in the morning, you have one clock that's showing to 'correct' time.
They are ONLY accurate when they get a signal to set themselfs, this is done ONCE every minute. It does not do the constant radio update all the time therefore it has to rely on the old quartz crystal that is as presice as your watch so to be honest it is ONLY spot on once it gets the nudge from the radio signal and after that for the next minute it just free runs.
Look 'ere www.npl.co.uk/time/msf.html
Now here is a good question. If the time delay on SKY is about 1.5 to 2 seconds out from the analogue signal when we all go digital what will be the correct time? Freeview or SKY?
>> Edited by scared but happy on Saturday 12th November 20:37
Look 'ere www.npl.co.uk/time/msf.html
Now here is a good question. If the time delay on SKY is about 1.5 to 2 seconds out from the analogue signal when we all go digital what will be the correct time? Freeview or SKY?
>> Edited by scared but happy on Saturday 12th November 20:37
scared but happy said:
They are ONLY accurate when they get a signal to set themselfs, this is done ONCE every minute. It does not do the constant radio update all the time therefore it has to rely on the old quartz crystal that is as presice as your watch so to be honest it is ONLY spot on once it gets the nudge from the radio signal and after that for the next minute it just free runs.
Look 'ere www.npl.co.uk/time/msf.html
Now here is a good question. If the time delay on SKY is about 1.5 to 2 seconds out from the analogue signal when we all go digital what will be the correct time? Freeview or SKY?
Neither!
Best general purpose source of accurate time is GPS. It has to be accurate, because that's the way it works.
benyeats said:That is the whole point, the atomic clock is accurate to one second in a million years if it is set, then let to run for a million years on its own, and it will only lose a second. But it will be re-set by its keepers time and time again. If these clocks/watches are getting an update every minute, then they will always be accurate. They will no more lose a second every million years than the atomic clock that they take their signal from. And that will not lose a second over a million years because it will not be left to run like that, it will be updated and re-set often too.
As someone else pointed out it must be the accuracy of the atomic clock that is 1 sec per million years. The radio bit is the reason they are accurate not any clever watch making trick.
Ben
So the marketing tag line for these products is bollox, that was my point. After all, these products arent going to be taking their signal from a device that has been set and will not be touched again for a million years, the device they take their signal from will also be updated. Which make you wonder why they advertise using a flaw that wont actually manifest itself in the product. Surely a better tag line would be 'Always accurate...PERIOD'
Balmoral Green said:
As someone else pointed out it must be the accuracy of the atomic clock that is 1 sec per million years. The radio bit is the reason they are accurate not any clever watch making trick.
Ben
So the marketing tag line for these products is bollox, that was my point. After all, these products arent going to be taking their signal from a device that has been set and will not be touched again for a million years, the device they take their signal from will also be updated. Which make you wonder why they advertise using a flaw that wont actually manifest itself in the product. Surely a better tag line would be 'Always accurate...PERIOD'
Not wishing to be critical, but wouldn't a thirteenth century clock maker, have thought that using an invisible radio signal from a huge tower hundreds of miles away with an atomic frequency standard as a reference, a bit miraculous.
And that doesn't include the fact that the miracle that does all of this was manufactured from sand, using printing techniques, very strong acids, and best of all ion implantation equipment.
The resultant machine has no moving parts, save for the electric charges and the microscopic motor. The whole thing need be no larger than one of the jewels of the thirteenth century clockmakers clock.
I think thats pretty blooming "fantashtic" myself.
>> Edited by dilbert on Saturday 12th November 21:25
Balmoral Green said:
I keep seeing these adverts for 'radio controlled' clocks and watches. But there is something that I dont understand. If it is indeed 'accurate to within one second in a million years', then why does it need to get a radio update to stay accurate? and if it gets a constant radio update and is always adjusting itself, then it doesnt need to be accurate at all, any cheap timekeeping mechanism will do, and if it is constantly updating to stay accurate, then how can it lose a second? even if it is in a million years. If it is 'updating' then it will be correct all the time.
I bet Dr Goodfellow would know the answer.
I think I can answer this one for you. The actual clock mechanism in the clock/watch is not actually any more or less accurate than a standard quartz movement- which would usually be accurate to within a couple of seconds per day anyway. So over the course of a month the mechanism could be a minute or more out.
However, the addition of the radio controlled correction technology ensures that it remains as close to spot on as possible.
The accuracy of a second per million years is effectivley the same as that of an atomic clock (although IIRC they are actually more accurate than that, but it doesn't sound so interesting in marketing terms).
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