This subpanel creates free points at the center of the arc that best approximates the input set of nodes, points or lines.

Here, three nodes selected produce a point at the center of the arc that they form.  Three input points would work similarly.

Here, two selected lines are used to determine the arc center.  Note that the curved line could also have been used alone.

For nodes and points input, a minimum of three must be selected.

For lines input, the selection must not all lie on a straight line.

An optional tolerance is available to verify whether the calculated best fit circle is sufficient.  If ignored, the best fit circle is always calculated.  Otherwise, an error is returned if the input entities are not all on the circle within the specified tolerance.