Coordinate positioning apparatus and method of operation

A method of transforming at least one probe signal from a contact probe into a spatial measurement value, the contact probe having a deflectable stylus and in which the at least one probe signal is indicative of the extent of deflection of the stylus, in which the contact probe is mounted on an articulated continuous scanning head of coordinate positioning machine which facilitates reorientation of the contact probe about at least one axis during the collection of measurements using the contact probe, comprising:

• converting the probe signal into a spatial value using at least one probe signal gain variation correction factor which is dependent on the orientation of the contact probe about the at least one axis.

A method of calibrating a contact probe having a deflectable stylus configured to provide at least one signal, which is indicative of the extent of deflection of the stylus, the contact probe being mounted on a coordinate positioning machine which facilitates reorientation of the contact probe about at least one axis, comprising:

• determining a common probe signal conversion model for transforming probe signals into spatial measurement values from measurement data obtained with the contact probe positioned at a plurality of different orientations about the at least one axis.