A method is described for calibrating apparatus including a measurement probe mounted on a machine, such as a machine tool. The machine is arranged to capture machine position data indicative of the position of the measurement probe and the measurement probe is arranged to capture probe data indicative of the position of a surface relative to the measurement probe. The measurement probe may be an analogue or scanning probe having a deflectable stylus. The first step of the method involves moving the measurement probe at a known speed relative to an artefact whilst capturing probe data and machine position data. In particular, the measurement probe is moved along a path that enables probe data to be captured that is indicative of the position of two or more points on the surface of the artefact relative to the measurement probe. A second step of the method comprises analyzing the machine position data and the probe data and determining from that data the relative delay in capturing probe data and machine position data (i.e. the so-called system delay).