Hi Viv,

From my quick scribbles on a scrap of paper, if the arc is of radius r and angle 2A the rectangle will be 2rSinA by r(1-CosA) at a distance of rCosA from the centre of the circle.

If you like, I can email my scribbles to you which should explain how I got there. I hope I didn't slip up, but I'm just off out. I will double check it later today.

Alan