Problem Statement

Finding the angle between two bearings is often confusing.[1]

Find the angle which is the result of the subtraction b2 - b1, where b1 and b2 are the bearings. Input bearings are expressed in the range   -180   to   +180   degrees. The  result  is also expressed in the range   -180   to   +180   degrees.

Compute the angle for the following pairs:

Allow the input bearings to be any (finite) value.

Let's start with the solution:

real    B1, B2, Ang;
[Text(0, "   Bearing 1       Bearing 2      Difference");
loop   [B1:= RlIn(1);
        B2:= RlIn(1);
        Ang:= B2 - B1;
        while Ang >  180. do Ang:= Ang - 360.;
        while Ang < -180. do Ang:= Ang + 360.;
        CrLf(0);
        RlOut(0, B1);  ChOut(0, 9);
        RlOut(0, B2);  ChOut(0, 9);
        RlOut(0, Ang);
       ];
]