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The key feature of this construction process is the use of the perpendicular bisector to generate a point that can be used to construct the circle arc that subsequently remains 'well behaved' when the inner circle has passed through the 180 degree turn point.

Try and construct the mid-point of the circle arc by other means (such as angle bisectors) to fully appreciate this issue.

This particular construction process had its first public debut at the Annual UK T3 Trainers Conference, July 2009.