A method of operating a coordinate positioning apparatus comprising an articulated head having at least one rotational axis. The method comprises, in any suitable order, loading at least one interchangeable task module onto the articulated head; and loading at least one interchangeable task module counterweight on the articulated head. The at least one interchangeable task module counterweight at least partially counterbalances the weight of the at least one task module on the articulated head about the at least one axis.