Method for recalibrating coordinate positioning apparatus

A method for measuring an object using a coordinate positioning apparatus comprising a platform, a measurement probe having a replaceable stylus, and a probe head for reorienting the measurement probe relative to the platform, the method comprising the steps of:

• (i) taking a first calibration data set for the coordinate positioning apparatus that comprises datum data for a plurality of orientations of the measurement probe, the first calibration data set defining a calibration of the coordinate positioning apparatus when the measurement probe comprises a first stylus, and the datum data including first datum data for a first nominal orientation of the measurement probe;
• (ii) replacing the first stylus of the measurement probe with a second stylus that is nominally identical to the first stylus;
• (iii) updating the first calibration data set to generate a second calibration data set that defines the calibration of the coordinate positioning apparatus when the measurement probe comprises the second stylus, the step (iii) comprising the steps of:
• (a) using the coordinate positioning apparatus to acquire one or more position measurements,
• (b) calculating a first correction from the one or more position measurements, the first correction describing any change in the first datum data following the replacement of the first stylus with the second stylus, and
• (c) updating the datum data for a plurality of different orientations of the measurement probe using the first correction to thereby generate the second calibration data set;
• and
• (iv) using the coordinate positioning apparatus, with the second calibration data set, to measure an object.