Poppies at Carlisle Castle

The installation of ceramic poppies that made such an impression 4 years ago at the Tower of London has been brought to Carlisle Castle this month. It is free to visit and is proving very popular. It is very thought-provoking. I was wondering about the way that the artist has modeled the curve from the top of the keep. From the outside I thought that it looked like a parabola. Careful measurement of the photograph shows that it goes out as far as it goes down so it is probably a section of a circle.