Circular scanning patterns

A method to compare similar physical areas of an inspection area using a circular scanner, the inspection area including a plurality of samples, the samples being substantially identical, the circular scanner having a stage apparatus, a drive mechanism, at least one scanning head and an axis of rotation, the at least one scanning head performing a circular scanning motion about the axis of rotation, the stage apparatus having at least two stage portions, the drive mechanism configured to provide relative movement between each of the stage portions and the axis of rotation, the method comprising the steps of:

• (a) mounting the samples on the stage apparatus such that there is one of the samples per one of the stage portions such that said samples are disposed symmetrically around the axis of rotation;
• (b) scanning at least part of the samples by employing the scanning head to perform a substantially circular scanning path;
• (c) comparing at least two best matched curved scan paths on said substantially circular scanning path by a pixel to pixel comparison;
• and
• (d) moving the samples relative to the axis of rotation such that said samples maintain a symmetrical disposition around the axis of rotation.