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    Re: A good clock for a few billion years
    From: Bill Lionheart
    Date: 2019 May 6, 10:03 +0100

    As an interesting twist on this the Argos system used for tracking
    whales, polar bears and ocean current beacons does involve the tracker
    transmitting, it uses Doppler shift like an EPIRBs (COSPAS-SARSAT).
    And yet often reporters and wildlife documentaries mistakenly call it
    "GPS tracking".
    On Mon, 6 May 2019 at 06:48, David C  wrote:
    > Geoff wrote
    > Thanks for the link Frank, but I'm afraid the author (Sophia Chen) has a 
    poor understanding of how GPS works, she wrote:
    > This is actually how GPS works. Satellites pinpoint your location on Earth 
    by precisely measuring how long it takes a radio signal to bounce from your 
    phone back to space
    > I  regularly read stories in the media which indicate that the author 
    believes that there is two-way communication between a gps receiver and the 
    > View and reply to this message

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