Syncing of Atomic G-Shock query.

[GuyIncognito]

I was in Lanzarote last week and took my G-Shock with me. I assumed with it being quite far from mainland Europe that it wouldn't sync or if it did sync it would set to mainland Europe time.
It actually synced every night and the time was correct for Lanzarote (same timezone as UK)
What's that all about?

[dkpw]

Not a lot in the way between Cumbria and Lanzarote...

The MSF radio signal is a dedicated standard-frequency and time broadcast that provides an accurate and reliable source of UK civil time. It is available 24 hours a day across the whole of the UK and beyond. The signal operates on a frequency of 60 kHz and carries a time and date code that can be received and decoded by a wide range of readily-available radio-controlled clocks.

The MSF signal is transmitted from Anthorn Radio Station in Cumbria by Babcock International, under contract to NPL. The signal covers the whole of the UK, and can also be received throughout most of northern and western Europe. It is monitored against the national time scale UTC(NPL) and corrected when necessary, ensuring that the transmitted time is always correct.

And if you didn't change your home city from London, you wouldn't see any change on the watch.

[Mitch]

I was in Lanzarote last week and took my G-Shock with me. I assumed with it being quite far from mainland Europe that it wouldn't sync or if it did sync it would set to mainland Europe time.
It actually synced every night and the time was correct for Lanzarote (same timezone as UK)
What's that all about?

You have your 'home city' set to London presumably and the watch will therefore look for the UK signal first. It may have actually found it but if it didn't it would then look for the German signal. if a signal is found the watch thinks you are in London and will set the time accordingly. If you want the watch to set to a different time zone you need to change your 'home city'.

The radio time signal is UTC, no matter which one is received and it is the watch itself which adjusts it to the correct timezone. Therefore you need to tell the watch where you are.



Mitch

[GuyIncognito]

Cheers. I was just surprised it synced down there.

[ColDaspin]

Daft question but, if these are radio waves, how does the receiving clock factor in the time taken for the signal to reach it?

[Mr Curta]

Daft question but, if these are radio waves, how does the receiving clock factor in the time taken for the signal to reach it?

Probably not too much of an issue at around 299,700 km/s

[ColDaspin]

Probably not too much of an issue at around 299,700 km/s

Thanks! I did say it was daft. For some dim reason, I thought they weren't EM waves.

[dkpw]

As Matthew says the speed of light is quite fast.

Here's a post I put up on WUS a while back about the accuracy of atomic syncing: How accurate is atomic syncing?


An interesting question, which has been playing at the forefront of my mind given my recent, frenzied spate of G-Shock purchases. These sync each night via radio so that they’re deadly accurate – but how accurate is accurate?

Luckily I didn’t have to work too hard to find the answer, as the hugely clever Mike Lombardi from the National Institute of Standards and Technology (NIST – the US standards agency responsible for time keeping) has written a paper answering my question.

However his paper has not just answered that initial, rather simplistic question. Instead he’s answered, in a beautifully clear and logical manner, all the other questions which us sad watch types would inevitably ask given the subject matter. It’s a tour de force and you can download it here.

Just in case you’re not convinced that you should read Mike’s paper for yourself – you should – I’ve set myself the task of summarising his four pages as succinctly as I can.

The “atomic” clocks that you and I can buy are not actually atomic, they are ordinary quartz watches or clocks.
They do however synchronise with a world-wide network of radio time signals.
The radio signals in turn are synchronised with Universal Time (UTC) which is generated by averaging many caesium and hydrogen atomic clocks around the world.
The difference between the radio signal and UTC is never more than 35 nanoseconds, put another way that’s a drift of 1 second every 30 million years!
It takes about 10 milliseconds for the radio waves to reach the watch, remember they travel at the speed of light.
It may then take a further 10 milliseconds for your watch to process the signal and synchronise.
Finally you need to take into account the accuracy of the quartz crystal, most are rated at +/- half a second a day.
So the answer to the question is, if your watch syncs daily it is always going to be better than half second off, since each sync brings it to within 50 milliseconds of UTC, or less than one second in 20 million years.

That’s impressive, although there’s always something new around the corner, in this case an atomic clock using a single ion of aluminium. It’s allegedly 100,000 times more accurate than current caesium clocks. Why would we need such accuracy? GPS technology relies on extremely accurate time keeping to determine locations precisely and improved accuracy could assist with space exploration and determining the effects of gravity.