Wizards now seem to be appearing that will find the centre and radius of a circle from three points on a arc. Can anyone help with the maths for this so that I can create the appropriate G code.

Is it possible to produce a modified centre finder in the shape of a sword, whereby the tips of the handles touch the arc at a fixed distance apart and the top of the handle slides to touch the arc. A datum line at centre of the sword then gives a reading of the radius and hence you have the centre and radius. A depth micrometer could possibly be modified. I do need the maths to try this though as I presume that the scale will be non-linear.

John