An articulated arm CMM comprises a plurality of transfer members, a plurality of articulation members connecting at least two transfer members to each other, a coordinate acquisition member at a distal end, and a base at a proximal end. The articulated arm CMM also comprises (1) a ratchet lock for restricting the motion of at least one transfer member in at least one direction of rotation and (2) a clutch mechanism for allowing limited rotation of the at least one transfer member upon application of a high amount of force upon at least one transfer member.