Thanks Ghenghis. I'll get busy on the white board next time I'm at work. I want to make sure that my logic/reasoning & equation set up is correct if I have to derive the technique. It's been 25 years since I last had to play silly buggers with slopes of a line. As I said, I used to have the (correct) formula for just this problem ie find a point on a line given slope & y-coordinate (plus offset if it didn't pass through the origin), memorised & noted down.
Last edited by Tinstaafl; 16th Feb 2005 at 15:54.