Surface sensor offset

A method of operating a coordinate positioning apparatus having a surface sensor that is rotatable about at least first and second perpendicular axes, the method comprising:

• positioning the surface sensor at a first angle about the first axis relative to a line that extends through the first axis and parallel to the second axis and obtaining a first measurement;
• positioning the surface sensor at a second angle about the first axis relative to a line that extends through the first axis and parallel to the second axis and obtaining a second measurement, the second angle being opposite in direction to the first angle relative to the first axis such that any offset of the surface sensor from an expected position will have at least a partially opposing affect on the first and second measurements;
• and
• using the first and second measurements to compensate for or establish the offset.

A method of operating a coordinate positioning apparatus having a surface sensor which is rotatable about at least a first axis, the method comprising:

• positioning the surface sensor at a first angular orientation and obtaining a first measurement by translationally moving the surface sensor;
• positioning the surface sensor at least at a second angular orientation and obtaining at least a second measurement by translationally moving the surface sensor, the second angular orientation being different to the first angular orientation such that any offset of the surface sensor from an expected position will have at least a partially opposing affect on the first and at least second measurements;
• and
• using the first and at least second measurements to compensate for or establish the offset.