ConcentricRings Dual Extruder Calibration

I made this pair of concentric rings as a test print for calibrating the x, y offset for my dual extruder setup.

The print on the left in the picture was made with rough guesstimates for the offset between the two nozzles. The (x,y) error was measured with the print still on the bed, and new offset values were calculated to result in perfect alignment in the second print, on the right.

Enjoy!