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    Re: A good clock for a few billion years
    From: Geoff Hitchcox
    Date: 2019 May 5, 18:39 -0700

    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.

    The GPS satellites transmit their own ephemeris (to give their position in space like that of a star), a GPS receiver creates multiple "Spheres of Position" and then minimises the "3D cocked hat" to adjust its own quartz clock to sync with atomic time. So then by trilateration it knows the 3D location of the receiver.

    A GPS receiver transmits no information to space, it has its own internal 'chart room' where it plays with 3d spheres - rather than the circles of position as with traditional 'Celestial Navigation'.

    Regards, Geoff Hitchcox, Christchurch, New Zealand.

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