(20S and 21S) Great Circle

[Dieter]

(06-03-2017 10:00 PM)Marcel Wrote:  For an other planet, the user must change the numerical factor!!!.. the radius of the planet in miles or km.

Since most planets are not perfect spheres there is not a single radius. For instance the WGS84 system (cf. GPS) works with an Earth radius of 6378,137 km in East-West direction and with 6356,7523 km for North-South.

Eddie's formula uses a constant radius of 3958,75 miles or 6371 km. This is a good choice that minimizes the error of the calculation (cf. here). Yet there still is a potential error of 0,5%. So the result should be rounded to at most three significant digits. For the given examples that's 6320 resp. 4940 miles.

A final hint: enter an angle, and 1 P→R simultaneously returns both sine (in Y) and cosine (in X).
Edit: this works on classic RPN calculators and probably cannot be used for the algebraic 20S and 21S.

Dieter