Originally Posted by

**hairymarmite** Unfortunately I did not measure the chord length on site assuming I had enough information already to cal the rest. I only have the arc length, and the height. I have been trying to calculate the chord length from the arc length and height alone. Surely there is only one chord length for a given height and arc length ? When I can calculate the chord length I can then use the equation you've given me (nice explanation by the way) to get the radius and the rest.

Am I missing something startlingly obvious perhaps to do with triangles within circles?