A computer-assisted medical device comprising: an articulated arm comprising a first joint; and a control unit coupled to the articulated arm and comprising one or more processors; wherein the control unit is configured to: switch the first joint (222, 228, 232, 236, 238, 242, 262, 264, 268, 272) from a locked state of the first joint (222, 228, 232, 236, 238, 242, 262, 264, 268, 272) to a float state of the first joint (222, 228, 232, 236, 238, 242, 262, 264, 268, 272) when a stimulus associated with the first joint (222, 228, 232, 236, 238, 242, 262, 264, 268, 272) exceeds a first unlock threshold, wherein movement of the first joint (222, 228, 232, 236, 238, 242, 262, 264, 268, 272) is restricted in the locked state of the first joint (222, 228, 232, 236, 238, 242, 262, 264, 268, 272) and movement is permitted in the float state of the first joint (222, 228, 232, 236, 238, 242, 262, 264, 268, 272); and switch the first joint (222, 228, 232, 236, 238, 242, 262, 264, 268, 272) from the float state to the locked state when a velocity associated with the first joint (222, 228, 232, 236, 238, 242, 262, 264, 268, 272) falls below a first lock threshold; characterised in that the first unlock threshold is based on a location of the first joint (222, 228, 232, 236, 238, 242, 262, 264, 268, 272) in the articulated arm; or the first lock threshold is based on the location of the first joint (222, 228, 232, 236, 238, 242, 262, 264, 268, 272) in the articulated arm. an articulated arm comprising a first joint; and a control unit coupled to the articulated arm and comprising one or more processors; wherein the control unit is configured to: switch the first joint (222, 228, 232, 236, 238, 242, 262, 264, 268, 272) from a locked state of the first joint (222, 228, 232, 236, 238, 242, 262, 264, 268, 272) to a float state of the first joint (222, 228, 232, 236, 238, 242, 262, 264, 268, 272) when a stimulus associated with the first joint (222, 228, 232, 236, 238, 242, 262, 264, 268, 272) exceeds a first unlock threshold, wherein movement of the first joint (222, 228, 232, 236, 238, 242, 262, 264, 268, 272) is restricted in the locked state of the first joint (222, 228, 232, 236, 238, 242, 262, 264, 268, 272) and movement is permitted in the float state of the first joint (222, 228, 232, 236, 238, 242, 262, 264, 268, 272); and switch the first joint (222, 228, 232, 236, 238, 242, 262, 264, 268, 272) from the float state to the locked state when a velocity associated with the first joint (222, 228, 232, 236, 238, 242, 262, 264, 268, 272) falls below a first lock threshold; characterised in that the first unlock threshold is based on a location of the first joint (222, 228, 232, 236, 238, 242, 262, 264, 268, 272) in the articulated arm; or the first lock threshold is based on the location of the first joint (222, 228, 232, 236, 238, 242, 262, 264, 268, 272) in the articulated arm. switch the first joint (222, 228, 232, 236, 238, 242, 262, 264, 268, 272) from a locked state of the first joint (222, 228, 232, 236, 238, 242, 262, 264, 268, 272) to a float state of the first joint (222, 228, 232, 236, 238, 242, 262, 264, 268, 272) when a stimulus associated with the first joint (222, 228, 232, 236, 238, 242, 262, 264, 268, 272) exceeds a first unlock threshold, wherein movement of the first joint (222, 228, 232, 236, 238, 242, 262, 264, 268, 272) is restricted in the locked state of the first joint (222, 228, 232, 236, 238, 242, 262, 264, 268, 272) and movement is permitted in the float state of the first joint (222, 228, 232, 236, 238, 242, 262, 264, 268, 272); and switch the first joint (222, 228, 232, 236, 238, 242, 262, 264, 268, 272) from the float state to the locked state when a velocity associated with the first joint (222, 228, 232, 236, 238, 242, 262, 264, 268, 272) falls below a first lock threshold; characterised in that the first unlock threshold is based on a location of the first joint (222, 228, 232, 236, 238, 242, 262, 264, 268, 272) in the articulated arm; or the first lock threshold is based on the location of the first joint (222, 228, 232, 236, 238, 242, 262, 264, 268, 272) in the articulated arm.