An articulated arm CMM comprising: an articulated arm comprising one or more articulated arm members, a coordinate acquisition member at a distal end, and a lower support assembly at a proximal end; and an arm support member mounted about the articulated arm CMM to support one or more articulated arm members during rotation, the arm support member comprising: a gear comprising circumferential teeth, an engagement member configured to reversibly engage the circumferential teeth of said gear to prevent rotation of the gear relative to the engagement member in at least a first direction of rotation, and a release member movable between a first position and a second position, wherein the release member prevents the reversible engagement between the engagement member and the gear when in the first position and does not prevent said reversible engagement when in the second position, such that the arm support member hinders rotation of the one or more articulated arm members when the lock release member is in the second position but does not when the lock release member is in the first position, and an actuator wherein the actuator is configured to receive an input to move the release member between the first position and the second position and wherein the actuator comprises a detent mechanism in cooperation with the lower support assembly wherein the detent mechanism can provide a user of the articulated arm CMM with at least one of a tactile, audible, and visual indicator when the locking mechanism is in an engaged or disengaged state. an articulated arm comprising one or more articulated arm members, a coordinate acquisition member at a distal end, and a lower support assembly at a proximal end; and an arm support member mounted about the articulated arm CMM to support one or more articulated arm members during rotation, the arm support member comprising: a gear comprising circumferential teeth, an engagement member configured to reversibly engage the circumferential teeth of said gear to prevent rotation of the gear relative to the engagement member in at least a first direction of rotation, and a release member movable between a first position and a second position, wherein the release member prevents the reversible engagement between the engagement member and the gear when in the first position and does not prevent said reversible engagement when in the second position, such that the arm support member hinders rotation of the one or more articulated arm members when the lock release member is in the second position but does not when the lock release member is in the first position, and a gear comprising circumferential teeth, an engagement member configured to reversibly engage the circumferential teeth of said gear to prevent rotation of the gear relative to the engagement member in at least a first direction of rotation, and a release member movable between a first position and a second position, wherein the release member prevents the reversible engagement between the engagement member and the gear when in the first position and does not prevent said reversible engagement when in the second position, such that the arm support member hinders rotation of the one or more articulated arm members when the lock release member is in the second position but does not when the lock release member is in the first position, and an actuator wherein the actuator is configured to receive an input to move the release member between the first position and the second position and wherein the actuator comprises a detent mechanism in cooperation with the lower support assembly wherein the detent mechanism can provide a user of the articulated arm CMM with at least one of a tactile, audible, and visual indicator when the locking mechanism is in an engaged or disengaged state. <EOS>