[LaggyLou]

Ok, I'm doing something wrong. Let's call X half the chord length and y the arc height. As I understand it:

R=(x^2+y^2)/y -- is that right?

Then:

Angle = 2*Arcsin(x/arc Radius) {Chord length = 2x, so the 2's in your formula cancel out, right?}

Arc Length = R * Angle


.... Ok, so here are some real numbers:

x=.419, y=.251

Radius = .9504
Angle = .9131, yielding
Arc Length = .8678

But I don't see how that could be right, because the length of the hypotnuse of a rt triangle with X and y as the legs is .488428. The arc length has to be more than double that hypontuse, doesn't it?