Hi Hamish

Are you coding for one more station than the number of stations, with index i ?
for example, if num_stations = 5, index i has the values 0, 1, 2, 3, 4, 5, which are six values.

I do not see all of the code. Maybe the second curve stations can be calculated in reverse order?

I've found .htm scripting to be more challenging, but the most recent methods I've used, (borrowed from MaxS), can really speed things up.

(Have not read your pdf's yet.)

- Brian