locator.rar

Hello,
I have problem with calculations of latitude and longitude in my programm. Programm work, but at the finnish, distance in km is wrong, for short distance it's +- 1-2 km wrong, and for long distance is +- 4-7 km wrong.
Programm calculate distance between grid squares (Maidenhead grid squares).

This is formula from IARU Region 1 VHF Committee:
Distance = 111,2 * arccos(sin Latitude1 * sin Latitude2 + cos Latitude1 * cos Latitude2 * cos(Longitude1-Longitude2))

where the conversion factor is 111,2 km/deg.

Points rounding methods:
Distance Commenced km Math Truncation
0 km 1 0 0
43,2 km 44 43 43
56,7 km 57 57 56

Please, can anyone look at my code and help me to found error in code?

Thank you very much in advance.