I’ll give an exemple to explain my “concern”. Before the flight, as normal, I fill up my Flight Plan. Then, I’ll see what heading I should follow in order to reach my first fixe. Let say that my “Bearing to Next” is showing “80*”.
But during cruise, and for the same fixe, this value will continually change (due to rounded shape of the earth I believe!).
So for a same fixe the value just after rotation can be 80* but turn to 130* few hours later.
In order to avoid checking every hours and having to change the heading very often, is there a way to plan in advance what will the “final value”?