This script calculates the distance between two locations, the latitude and longitude of which are known. The coordinates are given in decimal degrees. South latitudes and west longitudes are negative. The calculation formulae is so called great-circle distance calculation, which assumes a spherical earth. The accuracy of the calculation is not as perfect as in the more complicated Vincenty's formulae, which assumes the earth to be an oblate spheroid. The error is however under 0.3% in most cases.