<p>A method according to one embodiment of the invention may be performed using a calibration plate having at least one alignment marker and at least one height profile. First, the calibration plate is positioned using an alignment sensor. Then the height profile is measured by a height sensor. Then the calibration plate is rotated by substantially 180 degrees and the two operations are repeated. This procedure results in two measured height profiles, which are compared in order to find a best fit. The amount of shift performed to find the best fit is used to determine a distance between the alignment marker and the X,Y position of the measurement point of the height sensor.</p>
