More of the world DOESN'T have access to time signals than does. Europe, Japan and North America at present are it. Clocks, watches and such won't sync to shortwave,the stations are all longwave. So even where a shortwave time signal exists (China, for example), no longwave devices are possible. Also, unless a device is specifically designed to do so, it won't work outside it's 'home' territory as frequencies and methods of broadcast differ.

OK, so the final conclusion is that I will need to manually set the time for my gizmo.... thanks again to everyone for their feedback.

Related question.... does someone have a clue how (or if) I can change the Temperature reading on the Main Unit from degrees F to Celcius? Ive downloaded the manuals from the website but the manual says nothing about this. The remote sensor units do have a switch in the back panel where you can switch between C and F, but the main unit has no hardware setting for this.

Thanks.

415.767.2676 (415-PopCorn) will also work and it's just as exact . Actually, it's 415-767-any 4 digits.

While a GPS positioning fix necessarily depends on receiving signals from multiple GPS satellites, to get the right time you only need one.

To get high accuracy (nano seconds) you need to know
how old the GPS signal is. This cannot be done with just one
satellite signal.

http://tycho.usno.navy.mil/

The official time source for the United States and a number of other countries. I think they also provide GMT. At least the clocks at Greenwich say that they are calibrated by the Naval Observatory time. Due to time delays on the internets it wont be super precise, to the small fraction of a second, but its pretty unlikely that you will miss your flight because of the difference

Errr.... do you not think that, in the case of Greenwich, it might be the Royal Naval Observatory?

Not according to my recollection of the sign there on the clock. It said US Naval Observatory, Washington, DC.

Check it out this weekend if you get a chance I wont get a chance to check myself for a bit. Im in the UK at the end of the month but in Cambridge and on a tight schedule. I doubt I will have time to get there.

Wouldnt be the first time I had a faulty memory, but I remember because I was shocked when I saw it since my expectation was the same as yours.

While it's true that the data transmission from all satellites carries the time information (to be exact, the time at THAT satellite), most consumer GPS units won't decode and display that information. Until there are enought SV (satellites) received and decorrelated, the unit will most likely display the time that it's calculated based on time passed from the last fix. Now, when the unit has calculated it's position (minimum of 3 satellites for a 2-d fix, 4 for a 3-d fix), it will also have calculated the Zulu-time for the unit's location (all GPS time is in Zulu/GMT) and will display 'local' based on the device settings.

RFTraveler

Well, I'm shocked, shocked I tell you to read that In truth, it's some years since I've been to Greenwich, so my memory is probably more likely to be faulty.

So I had a quick google: http://wwp.greenwichmeantime.com/info/time.htm seems to confirm your observations.

But it gets much, much worse. Towards the bottom of http://www.greenwich-guide.org.uk/meridian.htm we find out that UTC is actually coordinated from France!

It turns out that we have our own atomic clock, as I'd thought, as do the Germans, you Americans and loads of other countries: http://www.atomicclockrugbymsf.co.uk/Atomic-clocks.htm (although I'm not sure how up to date this is, as I thought our clock had been moved from Rugby to elsewhere...).

But none of this explains why the US Naval Observatory gets a credit at Greenwich

Great explanation. ^ thank you.

Most people do not realize that the GPS signals take time to reach
you. The signals travel approximately at the speed of 1,079,252,848.8 km/h
and by the time they reach you, the time ticks are old already.
How old? you can only find out by comparing them to other ticks.

Alex, both my units have a hardware switch C/F - one on the front panel (weather forecaster) and one on the back (clock/temp). The weather forecaster also has barometric pressure mB/inHg switch on the front panel.

Which model do you have?

John

If your radio uses shortwave, you might be in luck. Many countries (at least used to) broadcast time on the same frequencies as the US. 2500, 5000, 10000, 15000 KHz. One wiki page mentions some radio frequencies currently used but definitely in the past there were MUCH more. There probably still are but it isn't listed.

http://en.wikipedia.org/wiki/Radio_clock

BTW, this reminds me of how warped I used to be, listening to those stations for hours at a time. "At the tone, __ hours ___ minutes coordinative universal time. BEEEEEM boom boom boom boom click click duuun click click click ". Especially funny was listening to both Colorado and Hawaii (or other countries) at the same time. Hours of entertainment indeed. The scary thing is that I enjoyed listening to it almost as much as listening to transpacific air traffic.

I don't believe it's "approximately". The metre/meter is defined as the distance light travels in 1/299 792 458 of a second, so the speed of light is exactly 1 079 252 848 800 m/h. Of course light slows down when it hits the atmosphere.

Greenwich is famous for GMT, which is a measure of the Earth's rotation. GMT is so irrelevant for GPS, which uses atomic time (one version of it is the UTC).

For those California numbers (Northern: 767-XXXX, Southern: 853-1212), it's only good if you get AT&T (formerly SBC, formerly Pacific Bell). If you live in Verizon (formerly GTE) territory, its version is no good. Calls from out of the area get connected to AT&T.