gcode for wincnc that finds the center of a circle

probe.nc

 G90
 G92

 [X probing]
 L210X [Switch low limit on X axis]
 [The m28 and g31 on the next line make WinCNC stop when the limit switch is hit instead of aborting like it normally would)
 l91 G1X-10 M28 G31 F30 [probe 10 inches in the negative X direction till we trigger the probe]
 l212 [switch limits back]
 l1 N28 V{AP0} [store current absolute position to register 28]
 l91g0X0.05 [back off a little]
 l211X [switch high limit on X axis]
 l91g1X10 m28 g31 f30 [probe 10 inches in positive X direction till we trigger the probe]
 l212 [switch limits back]
 l1 N29 V{AP0} [store absolute position to register 29]
 L91G0X-0.05 [back off]
 L90G0X{(PH28+PH29)/(2))} [Move to center in X direction]

 [Y Probing]
 L210Y [Switch low limit on Y axis]
 l91 G1Y-10 M28 G31 F30 [probe  10 inches in the negative Y direction till we trigger the probe]
 l212 [switch limits back]
 l1 N28 V{AP0} [store absolute position to register 28]
 l91g0Y0.05 [back off a little]
 l211Y [switch high limit on Y axis]
 l91g1Y10 m28 g31 f30 [probe 10 inchesin positive Y direction till we trigger the probe]
 l212 [switch limits back]
 l1 N29 V{AP0} [store absolute position to register 29]
 L90G0Y{(PH28+PH29)/(2))} [Move to center in Y direction]