Starpath DR Calculator Help

Great circle computations are discussed at

Great Circle Distance — The Three Options

In qtVlm you can change the radius in menu Config / Advanced / Earth radius
the one called "Celestial" is the spherical earth, with 1' = 1 nmi along any great circle

On the great circle result, the Heading is the initial heading. The actual heading changes along the route.

Rhumb line computations (Mercator sailing) is discussed in

Section 11.23 Rhumb-line Sailing

of our textbook Celestial Navigation: A Complete Home Study Course

We use the Bowditch Meridional Parts procedure, where we compute
the Parts using the equations presented in the Explanation of Table 6 that is found
on PDF page 16 of Volume 2 of the 2021 edition of Bowditch

Note that the app does not read the earth radius option for Rhumb Line computations.
It uses the ellipsoid values given in Bowditch.

NOTE: This calculator is build as a Progressive Web App (PWA), which means when downloaded to your mobile app and saved to the home screen it will work offshore with no network or internet connection. Once installed as a WPA, check that it woks in Airplane mode with W-IFI turned off.