That's a new calculator for measuring a distance between two cities - the first calculator of a new generation, that is able to use pre-stored reference data.
There is one algorithm for calculations and one infinite amount of data. This data stored in the reference book Cities Handbook
, where I already entered the coordinates for 4 cities. The main convenience is that after the addition of new coordinates to the reference book, which is possible to the registered users, this cities appear in the calculator.
By the way, loading of the data out of the reference book may take a while so if the graphs are empty - you have to wait a bit.