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    Re: GPS Anti Spoof app
    From: Frank Reed
    Date: 2017 Dec 4, 09:46 -0800

    Hewitt, you wrote:
    "this looks really good."

    Thanks. Please let me know what makes sense and what doesn't (especially from a beginner's point of view --which you are not, of course, but you know how to put yourself in a beginner's shoes, as is clear from your books)

    You asked:
    "Are "T adjust" and "seconds' delay" already in the UTC time on the display?"

    Yes, for the first, no, for the second. The number of seconds in "T adjust" is the app's best estimate of the system time error in your device. Typical Android devices have system clock errors up to five seconds when they have had recent cell network access. That time error can easily drift substantially when the devices are off-network for a while. The app checks the GPS time and uses that as an adjustment to the system time. The results are usually within a fraction of a second. So the displayed "UTC" is as advertised --the app's best estimate of actual UTC. Internally, the app also corrects for DUT (probably over-kill but it's included). This month, for example, the Earth's rotation time (UT1) is about a quarter of a second ahead of UTC. By the beginning of this summer, they will be nearly synchronized.

    The seconds delay feature is designed to make it easier for one person to use the app since you have to take your sextant sight and then look at the app. If you're able to hold a finger above the pause button and take your sextant sight at the same time, of if you can call "mark" and have an assistant tap pause, then you could set the delay to zero. But that's a circus! It's better to set a delay of ten seconds, and then count off ten before you press pause. The paused time will then show something like 17:50:46-10 which means that the displayed altitude was correct at 17:50:36.

    You also asked:
    "What is "Net Wx"?"

    If it's selected, the app will attempt to get online weather data so that you don't have to enter temperature and pressure manually. Of course the T/P correction is minimal for altitudes above 15°, but the app handles the correction easily and accurately. If you're off-network, you can enter temperature and pressure manually. Note that you may have to check "Net Wx" once in the settings and then come back to it to see that the numbers have changed. The app doesn't care.

    You concluded:
    "PS - I got the pro version. Someday I'll ask you to autograph it. "

    Great! Lots of stars available. You're one of the lucky two who upgraded. :)

    Frank Reed
    Clockwork Mapping
    Conanicut Island USA

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