QRB check calculation. The same formula is intergrated in cross check program.
Recommended by the IARU Region 1 VHF Committee (Noordwijkerhout, 1987), i.e. the formula proposed by PZK,
for calculating distances in VHF and Above Contests and the "commenced km" points rounding method (Lillehammer, 1999).
Distance = 111,2 * arccos(sin Latitude1 * sin Latitude2 + cos Latitude1 * cos Latitude2 * cos(Longitude1-Longitude2))
where the conversion factor is 111,2 km/deg.