A sensor for measuring three orthogonal external forces and torques, comprising: a load-bearing member having a longitudinal axis extending in a first direction; and a plurality of strain gauges (20, 22, 23) including a first and a second strain gauge mounted on a surface of the load-bearing member, wherein: the first and second strain gauges are symmetrically disposed about a line of symmetry on the surface of the load-bearing member, the line of symmetry extending substantially in the first direction; and a sensing axis of the first strain gauge is angularly offset from the line of symmetry by a first angle having a value between zero and 90°; wherein a sensing axis of the second strain gauge is angularly offset from the line of symmetry by a second angle substantially equal in magnitude to and substantially opposite in direction from the first angle; characterised by further comprising: a third, a fourth, a fifth, and a sixth strain gauge mounted on the surface of the load-bearing member, wherein: the third and fourth strain gauges are symmetrically disposed about a second line of symmetry on the surface of the load-bearing member; the second line of symmetry extends substantially in the first direction; the fifth and sixth strain gauges are symmetrically disposed about a third line of symmetry on the surface of the load-bearing member; and the third line of symmetry extends substantially in the first direction. a load-bearing member having a longitudinal axis extending in a first direction; and a plurality of strain gauges (20, 22, 23) including a first and a second strain gauge mounted on a surface of the load-bearing member, wherein: the first and second strain gauges are symmetrically disposed about a line of symmetry on the surface of the load-bearing member, the line of symmetry extending substantially in the first direction; and a sensing axis of the first strain gauge is angularly offset from the line of symmetry by a first angle having a value between zero and 90°; wherein a sensing axis of the second strain gauge is angularly offset from the line of symmetry by a second angle substantially equal in magnitude to and substantially opposite in direction from the first angle; characterised by further comprising: a third, a fourth, a fifth, and a sixth strain gauge mounted on the surface of the load-bearing member, wherein: the third and fourth strain gauges are symmetrically disposed about a second line of symmetry on the surface of the load-bearing member; the second line of symmetry extends substantially in the first direction; the fifth and sixth strain gauges are symmetrically disposed about a third line of symmetry on the surface of the load-bearing member; and the third line of symmetry extends substantially in the first direction. the first and second strain gauges are symmetrically disposed about a line of symmetry on the surface of the load-bearing member, the line of symmetry extending substantially in the first direction; and a sensing axis of the first strain gauge is angularly offset from the line of symmetry by a first angle having a value between zero and 90°; wherein a sensing axis of the second strain gauge is angularly offset from the line of symmetry by a second angle substantially equal in magnitude to and substantially opposite in direction from the first angle; characterised by further comprising: a third, a fourth, a fifth, and a sixth strain gauge mounted on the surface of the load-bearing member, wherein: the third and fourth strain gauges are symmetrically disposed about a second line of symmetry on the surface of the load-bearing member; the second line of symmetry extends substantially in the first direction; the fifth and sixth strain gauges are symmetrically disposed about a third line of symmetry on the surface of the load-bearing member; and the third line of symmetry extends substantially in the first direction. a third, a fourth, a fifth, and a sixth strain gauge mounted on the surface of the load-bearing member, wherein: the third and fourth strain gauges are symmetrically disposed about a second line of symmetry on the surface of the load-bearing member; the second line of symmetry extends substantially in the first direction; the fifth and sixth strain gauges are symmetrically disposed about a third line of symmetry on the surface of the load-bearing member; and the third line of symmetry extends substantially in the first direction.