A series of nominally identical production workpieces are measured on a workshop coordinate measuring apparatus. They are corrected using correction values generated by comparing coordinate values of a reference workpiece measured on the workshop apparatus with corresponding values derived from external measurements. To reduce the care and skill required, the external measurements are used to determine reference values of a geometric property of a feature of the reference workpiece, rather than coordinate values corresponding directly to those made on the workshop apparatus. Corresponding coordinate values are then generated from knowledge of the perfect form of the feature of the reference workpiece.