>By the way
>
>You are using a constant 3958.75586574. I believe this is the radius of the earth in miles. If you want km, I'd use 6371
>
>Source - http://www.movable-type.co.uk/scripts/latlong-db.html

George suggests to use

I would recommend that you allow the calculations to process the data using miles. If you want the results in KM, simply multiply values by 1.609344. You could modify the CalculateDistance function to multiply by this value just prior to returning.

but I don't see how did he arrive to the constants used in these formulas (I assume Michel used his scripts).