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    Re: Choice of timepiece
    From: Lu Abel
    Date: 2009 Nov 13, 19:59 -0800

    Not to start a controversy (especially with you!), but I'm looking at 
    heavens-above.com and its display is about seven seconds slower than 
    time.gov.  I suspect that while, as they claim, they have very accurate 
    time-keeping on their server, they're not compensating for propagation 
    delay across the Internet.  
    I just held my WWVL clock up to the time.gov display and it looks like 
    my Internet time is a tiny fraction of a second faster than my clock.   
    Mis-estimate of the delay to my computer by time.gov, or a display lag 
    (ala Doug's Trimble) on the part of my 
    $5.00-on-sale-at-the-local-electronics-superstore clock??
    frankreed@HistoricalAtlas.com wrote:
    > Douglas Denny, you wrote:
    > "I can understand too that modern GPS engines are going to calculate faster 
    and so give less delay - but nevertheless there is no excuse whatever that 
    the display time can, with no effort needed by the designer, be _exact_ and 
    displayed as such or flagged as U/S until correct.  It is really rather silly 
    to have a piece of kit which receives signals of time to within a few 
    nanoseconds, knows it,  and cannot display it accurately"
    > But this is just a market demand issue (and market demand drives product 
    specifications, right?). The vast majority of GPS users are looking for 
    position information primarily, and the time from the device is just a bonus. 
    Very few GPS users require time accurate to the nearest five seconds, let 
    alone the nearest tenth of a second. Who would use that information in a 
    handheld GPS unit or any unit designed fundamentally for position-finding? Of 
    course, there are entirely different market segments out there, like mobile 
    phone companies, for whom the exact time is actually the most important 
    product in the GPS signal. It all comes down to demand. I agree that it's 
    ironic that the exact time is in there, hidden away somewhere, but I don't 
    agree that it's "silly" we can't see it. It's like my previous cell phone 
    which had a GPS receiver and knew its position accurately but had no way to 
    display it (this was a marketing choice by the manufacturer and the service 
    provider). But it DID have extremely exact time displayed --accurate to the 
    nearest tenth of a second quite reliably. This was derived from the cell 
    towers' clocks apparently, and presumably the towers got it from specialty 
    GPS hardware.
    > On the other topic in this thread, Internet time can be very good. One of my 
    favorite older web sites, the satellite tracking site at 
    www.heavens-above.com, recently added a little tool that provides properly 
    synchronized time accurate to "better than" one tenth of a second. I tested 
    it from my PC against WWV just tonight, and it seemed to be that accurate. 
    Then I tested the same web page from the web browser in my current smartphone 
    (two years old so therefore "a dinosaur"). That same tool in the phone 
    browser could not keep up. The initial time was about right, but the ticking 
    seconds after that were in some kind of time warp and fell thirty seconds 
    behind after one minute. The phone's internal time (not from the Internet) 
    can be up to fifteen seconds off which is not good enough for celestial 
    navigation experiments, but certainly good enough for any practical tasks I 
    do in my day.
    > -FER
    > >
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