A coordinate positioning machine or CPM comprises a structure 22 moveable within a working volume 34, a drive arrangement 28 moves the structure around the working volume in fewer than six degrees of freedom, and a metrology arrangement 26 measures the position of the structure within the working volume in more degrees of freedom than the drive arrangement 28. The metrology arrangement may be a hexapod adapted to measure the position in six degrees of freedom. It may have six parallel measurement transducers providing six measurements, being disposed on six extendable legs. The drive arrangement may move the structure in three translational degrees of freedom and comprise a parallel plurality of actuators. The drive mechanism may be linear, with two parallel rods to maintain constant orientation, or rotary. It may be coupled to the metrology arrangement in a way that prevents distortion associated with the drive arrangement being transferred to the metrology arrangement. In use, the moveable structure would carry a tool, for example a surface sensing device such as a measurement probe 30 in the case where the machine is a coordinate measuring machine.
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