The calculation is currently based on sea level on a spheroid of r 3959 miles. The ability to enter your own formulas is something I have considered, but as the baseline that seems to be in dispute is the generally accepted one, i chose that. Of course it requires you either manually account for your own altitude or work at sea level.
Some have asked for a setting to enter the observer altitude.
@David, speed of the sun.. ok thats a possible one though I guess a more advanced function for people doing shorter range observations?
As I said, any suggestions welcome.
If there are any particular formulas that people use regularly they would like including in the App's setup I will be happy to publish an update.
Cheers