Basically the coffin bone follows closely a proportional development. Once you can identify the tip of p3 and the wings you can then use a golden ratio caliper to find a point that is very close to the mechanical center of rotation of the coffin joint. It has long since been known that managing the forces around the coffin joint are very important and identifying this point on the foot surface can be very consistent. It correlates well with other reported mapping protocols. It commonly lines up with the trimmed bars and widest part of the white line.