How can you have code that looks like that, and use a phrase like "implement it into the CalculateDistance subroutine"? I guess you have found code somewhere that is doing almost what you want and you wish to bend it to fit? Something like:

    ++$count if CalculateDistance (54.988056, -1.619444, @data{@SList[
+1 .. 2]}) > $x;
[download]

inside your while loop should be the trick.