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Live now, for Android and iOS/iPadOS devices... There are new versions of GPS Anti Spoof and GPS Anti Spoof Pro available which provide some minor updates and maintenance. There are some modest improvements in the quality of the temperature and pressure data for observer who have network access. As always, if you're off-network, or if you think you have better information, you can set the temperature and pressure manually.

How do you get this update if you have a prior version? It will come to you automatically in most cases, but you can always update sooner by visiting the app store for your app.

From the last update:
The option to turn off the "DOV Correction" which I saw mostly as a tool to educate users on the existence of the DOV Correction has been replaced by an "SI Units" selector. So now you can see Height of Eye in meters, temperature in °C and pressure in hPa (also known as mb, millibars). Weather data, as before, can be downloaded automatically from the internet if the "Wx" option is selected. 

Height of Eye works a little differently now. Behind the scenes it's the actual dip correction in gradations of tenths of a minute of arc. The displayed height is calculated from that. So you can enter a height of eye of 9.6 feet or 10.2 feet, equivalently 2.9m or 3.1 meters, but you can't enter exactly 10 feet or 3 meters. With any luck, this gets you thinking! Note that dip values less than 1.0 minutes of arc are not available except 0.0 exactly. 

The DOV or "deflection of the vertical" correction is still included, and a tag indicating its value will appear whenever the DOV is larger than a tenth of a minute of arc. 

What's the purpose of this app?
Option 1: If you're an experience celestial navigator and you suspect GPS Spoofing, a rare but growing threat, then you can detect it with a quick sextant sight of the Sun or another celestial body compared against the app's predicted altitude which is calculated with highest possible accuracy from the current GPS position. No paperwork, no other effort, no almanac, no sight reduction. Just take the sight and compare. If they match, you can sail with confidence. If they disagree, beware. The stars aren't perfect, but the stars don't lie. You can detect GPS Spoofing with a sextant and this app.

Option 2: If you are learning or practicing celestial and have no reason to suspect spoofing, then trust the GPS/GNSS satellites and use the app for instant feedback on your sights. Shoot the Sun or a star and compare. With no annoying paper and pencil work, you get instant feedback on your sights. If they match within a few tenths of a minute of arc, you're doing great. If your sight disagrees with the predicted value by more than a minute or two, then you have something to work on. There's no better way to gain skill and confidence when you're learning to take sextant sights than instant feedback from this app.

Read more and follow the links to the app stores here:
ReedNavigation.com/GPSantiSpoof/

Frank Reed
Clockwork Mapping / ReedNavigation.com
Conanicut Island USA