Surface measurement apparatus and method

A metrological apparatus has a mover (9) to carry out a measurement by effecting relative movement in a measurement direction between a workpiece support surface (16) and a stylus (11) such that the stylus is deflected as a stylus tip of the stylus follows surface variations along a measurement path on a workpiece surface. A data processor is configured to define a representation of the stylus using stylus characteristics data, to receive nominal form data, to simulate relative movement of the stylus representation and the nominal form along a measurement path, to identify any measurement points along the measurement path for which the relative locations of the stylus representation and the nominal form are undesirable, and to output to a resource data alerting an operator in the event of determination of a measurement point for which the relative locations of the stylus representation and the nominal form are undesirable.