Polynesian Navigation

'On a clear day, you can always see the sun
and with that sun, you never need to be truly lost'
(Mine)
'On a clear night, you could never lose the stars,
and with them you could never be truly lost'
(David Baldacci)

The Harp
In 1946 Harold Getty wrote a book called 'The Raft Book'. His aim was to write a manual for 'LifeBoat Navigation'. A manual that all ships would carry in their lifeboats. The manual would assist navigators who had the misfortune to have to abandon ship and find their way to land.
The story inspired me to design an app that would be available to everyone who would ever be in the same unfortunate circumstances, or for those who had the misfortune, for some reason, to be without a GPS.
I decided to design the app to incorporate some of the methods the Polynesians used and also to design some method to find land without the aid of a 'professional' sextant or GPS.
Most importantly, the app had to be useful for people with no real prior learned skills.
This App describes 'the Harp', a DIY sextant.
Two simple calculations are included for finding ones Latitude and Longitude.
Also two more calculations to navigate the Polynesian Way.
The Polynesian Navigators knew their hemisphere so well that they naivigated by it without any instruments. This App will take the place of that knowledge. All you need is an accurate time piece, e.g. your phone or a watch (set to GMT)

The first calculation is a 'Starfinder', that finds and identifies the 58 stars which are used by the Nautical Almanac.

The second calculation is that of a star's Sub-point. The stars Sub-point is the projected position directly underneath the star when the star is overhead, so that it's Declination and Right Ascension translate into latitude and longitude respectively.

If one has nothing else to navigate by, then the stars and a watch may give you some comfort that 'as Baldacci says' you should never be truly lost.
I hope you will enjoy this App!
PS
I assume that you are keeping track of a Dead Reckoning position.
You can find my simple Mercator App on Google Play (free):https://play.google.com/store/apps/details?id=com.mercatorapp.mercatorapp