Method and apparatus for inspecting workpieces

A method of operating a coordinate measuring apparatus with a reference workpiece which is one of a series of nominally identical workpieces to be inspected, the reference workpiece having at least one feature having a shape associated therewith, the method comprising:

• using the coordinate measuring apparatus to measure said feature of the reference workpiece at a plurality of measurement points, producing a set of measured coordinate values, and
• generating a set of measurement correction values associated with respective values in the set of measured coordinate values,
• wherein
• the shape associated with the feature is known not to deviate substantially from a perfect form,
• a value defining a size, position or orientation of the shape associated with the feature is known from measurement of the feature externally of the coordinate measuring apparatus, and
• the measurement correction values are generated from the measured coordinate values, from the known value of the size, position or orientation of the shape associated with the feature, and from the fact that the shape is known not to deviate substantially from the perfect form.