Patent ID: 8756973

Claim:
A method of operating a coordinate positioning apparatus having an articulated head on which a surface sensor is mounted, the articulated head providing for rotation of the surface sensor about at least first and second axes, the method comprising: positioning the surface sensor at a first angular orientation about the articulated head's first axis and obtaining a first measurement of an artifact with the surface sensor at the first angular orientation which comprises actuating the articulated head to rotate the surface sensor about the articulated head's second axis; driving the articulated head to position the surface sensor at a second angular orientation about the first axis and obtaining at least a second measurement of the artifact with the surface sensor at the second angular orientation which comprises actuating the articulated head to rotate the surface sensor about the articulated head's second axis, the first and second angular orientations being different from each other such that any offset of the surface sensor from an expected position will have at least a partially opposing effect on the first and second measurements; and using the first and second measurements to establish the offset of the surface sensor from the expected position, and using the offset to correct errors in subsequent measurements obtained by the surface sensor.