Apparatus for a co-ordinate positioning machine is described that comprises an articulating probe head for supporting a measurement probe. The articulating probe head comprises at least one electric motor. Heating means are provided for generating heat in the articulating probe head. The heating means may be the motors or discrete heating elements. Temperature sensing means, such as one or more temperature sensors, is also provided for determining the temperature at the articulating probe head. The apparatus allows the temperature of the articulating probe head to be controlled.