1. Method of determining the position of the center of a circular object with a known diameter on a generally flat surface comprising the steps of: sequentially moving a sensor along a plurality of know paths proximate said surface, each said path comprising a line portion, with the greatest distance between two adjacent line portions being less than the radius of said circular object; measuring the position of the sensor at two points in the same line portion where said sensor passes over the circumference of said object between said sensor and said surfaces; and calculating the position of the center of said object using the measured positions of the sensor at said two points.