NavList:

Jim Rives:

Have you tried my GPS Anti Spoof app yet? It's primarily intended as a celestial test to detect GPS Spoofing, but under conditions where you're not worried about spoofing, it's an excellent fast test of your sextant sights. Great for beginners but also useful for experienced observers who just want to see how well they're doing or want to test results under varying horizon conditions like with those "floating islands" that you've seen. The app tells you exactly what your sextant should read from your location, no calculations, no paperwork. Any difference between the display and your observatiojn is your error (or equivalently your intercept from the GPS position as AP).

From my website:

Get my new app. Defeats GPS Spoofing and great for sight-training, too: instant feedback with no paperwork at all. There's a standard version (free on Android, inexpensive on iPhone/iPad) that works with Sun, Venus, and Polaris sights and can function for three to seven days without network access. If you're serious about your navigation, then get the PRO version which includes the Sun, Moon, Venus, Mars, Jupiter, Saturn, Polaris and all 57 standard "navigational stars" and works offshore and off-network for months at a time.

• GPS Anti Spoof Pro for iPhone/iPad and Android.
• GPS Anti Spoof (standard) for iPhone/iPad and Android.

Frank Reed