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  • FIRST POST
    • Stevekir
    • By Stevekir 12th Jan 19, 4:36 PM
    • 4Posts
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    Stevekir
    UTC or GMT - which is mose accurate?
    • #1
    • 12th Jan 19, 4:36 PM
    UTC or GMT - which is mose accurate? 12th Jan 19 at 4:36 PM
    I have bought a good quality digital quartz watch and want to check its accuracy. Having set it exactly to a GMT signal on Worldtimserver.com and checking several times a day I notice that the watch changed from 0 (as set) to 1 second slow (varying over 5 to 10 minute periods) to now, 30 hours later it is 4 secs fast (varying over 5 minute periods by +-1 sec.) This variation is disappointing. However, I checked the accuracy of another, much cheaper, quartz digital watch and its timekeeping wandered in exactly the same way over the same 30 hours. It seems unlikely that both watches vary in exactly the same way..

    So I wondered if the GMT signal as broadcast itself wavered. To check, I am now timing both watched on UTC as on its site on the Internet and so far the the above variation is absent. I think I will stick to UTC.

    What do you think is going on please? Thanks.
    Last edited by Stevekir; 12-01-2019 at 4:55 PM.
Page 1
    • unforeseen
    • By unforeseen 12th Jan 19, 4:43 PM
    • 3,585 Posts
    • 4,782 Thanks
    unforeseen
    • #2
    • 12th Jan 19, 4:43 PM
    • #2
    • 12th Jan 19, 4:43 PM
    UTC = GMT. Any discrepancies are due to delays in the method of transmission or similar and not the time itself.

    You normally find that if you set to GMT your device will adjust itself for BST but not if UTC.
    • Stevekir
    • By Stevekir 12th Jan 19, 5:01 PM
    • 4 Posts
    • 0 Thanks
    Stevekir
    • #3
    • 12th Jan 19, 5:01 PM
    • #3
    • 12th Jan 19, 5:01 PM
    Thanks. I'm not using a device. I'm comparing the time (GMT or UTC) as shown on their sites, with the watch seconds hand as it goes round.


    Therefore, can I assume that the UTC I am seeing is fully accurate, or is it also varying due to transmission time delays etc?


    Thanks.
    • alanwsg
    • By alanwsg 12th Jan 19, 5:06 PM
    • 536 Posts
    • 234 Thanks
    alanwsg
    • #4
    • 12th Jan 19, 5:06 PM
    • #4
    • 12th Jan 19, 5:06 PM
    They'll both be subject to delays across the internet.

    The most accurate time source the average person will have access to is a locked-on GPS receiver showing the time (The satellites have seriously accurate clocks on board).

    Try downloading a GPS app that shows the time (e.g. GPS Test) and use the time displayed on that.
    • unforeseen
    • By unforeseen 12th Jan 19, 6:50 PM
    • 3,585 Posts
    • 4,782 Thanks
    unforeseen
    • #5
    • 12th Jan 19, 6:50 PM
    • #5
    • 12th Jan 19, 6:50 PM
    Thanks. I'm not using a device. I'm comparing the time (GMT or UTC) as shown on their sites, with the watch seconds hand as it goes round.


    Therefore, can I assume that the UTC I am seeing is fully accurate, or is it also varying due to transmission time delays etc?


    Thanks.
    Originally posted by Stevekir
    You are not accessing the times directly. As has been suggested either a GPS receiver or a good quality radio clock (one where you can also set your distance from the time source) . Both of these will supply UTC
    • John Gray
    • By John Gray 12th Jan 19, 8:33 PM
    • 5,395 Posts
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    John Gray
    • #6
    • 12th Jan 19, 8:33 PM
    • #6
    • 12th Jan 19, 8:33 PM
    You might get a closer accuracy for a time signal by telephoning 123 from a landline. Using a mobile will include propagation delays...
    • John Gray
    • By John Gray 12th Jan 19, 8:35 PM
    • 5,395 Posts
    • 3,188 Thanks
    John Gray
    • #7
    • 12th Jan 19, 8:35 PM
    • #7
    • 12th Jan 19, 8:35 PM
    ... a good quality radio clock (one where you can also set your distance from the time source) .
    Originally posted by unforeseen
    Please can you explain what difference the distance makes, given the speed of light?!
    • unforeseen
    • By unforeseen 12th Jan 19, 9:36 PM
    • 3,585 Posts
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    unforeseen
    • #8
    • 12th Jan 19, 9:36 PM
    • #8
    • 12th Jan 19, 9:36 PM
    Sorry, I'm used to using it as a reference in radar systems where an error of just 10 microseconds gives a range error of one mile and also an error of a few milliseconds flags the return as stale.
    • Tarambor
    • By Tarambor 13th Jan 19, 12:15 AM
    • 4,681 Posts
    • 3,592 Thanks
    Tarambor
    • #9
    • 13th Jan 19, 12:15 AM
    • #9
    • 13th Jan 19, 12:15 AM
    Please can you explain what difference the distance makes, given the speed of light?!
    Originally posted by John Gray
    Even at the speed of light they travel 185 miles a second. If you're getting a time signal from WWV which is US based then you could be receiving the signal over 30 seconds after it has been transmitted.
    • Slithery
    • By Slithery 13th Jan 19, 12:37 AM
    • 1,326 Posts
    • 2,065 Thanks
    Slithery
    If you need an accurate clock then get a Linux machine running ntpd with a GPS receiver attached then sync all of your clients directly from it.

    It's the only way to be sure...
    • tempus_fugit
    • By tempus_fugit 13th Jan 19, 12:46 AM
    • 582 Posts
    • 535 Thanks
    tempus_fugit
    Even at the speed of light they travel 185 miles a second. If you're getting a time signal from WWV which is US based then you could be receiving the signal over 30 seconds after it has been transmitted.
    Originally posted by Tarambor
    I think you mean 185,000 miles a second. Light can get to the moon and back in just a few seconds.
    Retired at age 56 after having "light bulb moment" due to reading MSE and its forums. Have been converted to the "budget to zero" concept and use YNAB for all monthly budgeting and long term goals.
    • John Gray
    • By John Gray 13th Jan 19, 7:40 AM
    • 5,395 Posts
    • 3,188 Thanks
    John Gray
    If you need an accurate clock then get a Linux machine running ntpd with a GPS receiver attached then sync all of your clients directly from it. It's the only way to be sure...
    Originally posted by Slithery
    Something like this, you mean?
    • chiny
    • By chiny 13th Jan 19, 8:34 AM
    • 143 Posts
    • 50 Thanks
    chiny
    Something like this, you mean?
    Originally posted by John Gray
    Eek, no... not on MSE Cheapskates here use a Raspberry Pi, with a USB GPS from Banggood (although a GPS HAT would be better) and open source ntp. Something like this. It works better by being placed in a bubblewrap envelope. Accuracy is usually within one microsecond.

    A little OTT perhaps...
    • Frozen_up_north
    • By Frozen_up_north 13th Jan 19, 10:54 AM
    • 1,806 Posts
    • 913 Thanks
    Frozen_up_north
    Anyone with an analogue communications receiver can listen to time signals easily, it’s how clocks on ships were set before GPS. Beware that radios incorporating DSP (digital signal processing) either in the radio itself or if listening via a computer will add delay to the pips.

    MSF, in the UK, on 60KHz and RWM from Moscow on 4996KHz and 9996KHz, give a pip every second with a different one each minute.

    For a list of these stations see: https://www.meinbergglobal.com/english/glossary/time-signal-transmitter.htm

    You can listen via a web based receiver in Holland, although the pips will be delayed and not accurate. This is the web site for listening on a smart phone, it works on my iPhone: websdr.ewi.utwente.nl:8901/m.html

    In the drop down box select CW and in the frequency box enter 60 (KHz) and you will hear MSF on 60KHz. MSF is audible 24 hours a day on that site, RWM is strong this morning on 9996. Don’t forget that listening via the web will delay the transmission by several seconds.
    • RumRat
    • By RumRat 13th Jan 19, 1:20 PM
    • 3,102 Posts
    • 1,874 Thanks
    RumRat
    Why the obsession? Is the watch going to be used for something that needs pin point accuracy? I doubt it....It'll be looked at 5 or 6 times a day and the second hand will be ignored totally......
    Life will have passed by quickly enough without checking on it's progress every 5 minutes....
    Drinking Rum before 10am makes you
    A PIRATE
    Not an Alcoholic...!
    • unforeseen
    • By unforeseen 13th Jan 19, 1:43 PM
    • 3,585 Posts
    • 4,782 Thanks
    unforeseen
    The only reason that I have radio controlled clocks and watches is because it means less clocks to adjust twice a year. Now if I can get my oven and microwave to incorporate RC clocks then I'd be happy - no more adjustments even after power cuts.
    • onomatopoeia99
    • By onomatopoeia99 13th Jan 19, 1:44 PM
    • 5,330 Posts
    • 11,939 Thanks
    onomatopoeia99
    Even at the speed of light they travel 185 miles a second. If you're getting a time signal from WWV which is US based then you could be receiving the signal over 30 seconds after it has been transmitted.
    Originally posted by Tarambor
    Oh my . So much error!



    I know there are delays when they are interviewing people in the US on the news, but that's a couple of seconds and due to the signal being bounced off satellites in geostationary orbit (which would need over 100 seconds just to reach the satellite at the value of c you posit).
    INTP, nerd, libertarian and scifi geek. Home is where my books are.

    5.2kWp system, SE facing, >1% shading, installed March 2019.
    • Frozen_up_north
    • By Frozen_up_north 13th Jan 19, 1:48 PM
    • 1,806 Posts
    • 913 Thanks
    Frozen_up_north
    Now if I can get my oven and microwave to incorporate RC clocks then I'd be happy - no more adjustments even after power cuts.
    Originally posted by unforeseen
    After a power cut, on our Panasonic microwave you hit the “Stop/Cancel” button and it then just displays “:”... job done, easy. Who needs a clock on every kitchen appliance? It’s so last century.
    • John Gray
    • By John Gray 13th Jan 19, 1:57 PM
    • 5,395 Posts
    • 3,188 Thanks
    John Gray
    Who needs a clock on every kitchen appliance? It’s so last century.
    Originally posted by Frozen_up_north
    I agree! When all our appliances are connected to the internet I hope they can all use NTP to get the time correct to the nearest fraction of a second! No possibility then of burnt toast!
    • unforeseen
    • By unforeseen 13th Jan 19, 2:52 PM
    • 3,585 Posts
    • 4,782 Thanks
    unforeseen
    After a power cut, on our Panasonic microwave you hit the “Stop/Cancel” button and it then just displays “:”... job done, easy. Who needs a clock on every kitchen appliance? It’s so last century.
    Originally posted by Frozen_up_north
    You do if you want it to start cooking at a set time without you being present.
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