A method of measuring residual torque in a previously tightened fastener, the method comprising: applying torque to a previously tightened fastener using a device adapted to measure applied torque and angular motion; and measuring torque applied to the fastener at a plurality of sensed angular positions to obtain a plurality of torque-angle data points, the method being characterised by: determining a base slope for at least one of the plurality of torque-angle data points, wherein the base slope comprises a change in torque over a change in angle for the at least one torque-angle data point as compared to a base point; determining a forward slope for the at least one torque-data point, wherein the forward slope comprises a change in torque over a change in angle for a point subsequent the at least one torque-angle data point and the at least one torque-angle data point; determining a slope delta for the at least one torque-angle data point, wherein the slope delta comprises a rate of change between the forward slope and the base slope; and comparing the slope delta of the at least one torque-angle data point to a minimum slope delta, thereby obtaining an indication of a rate of change of torque per unit of angular motion of the at least one torque-angle data point as compared to the plurality of torque-angle data points. applying torque to a previously tightened fastener using a device adapted to measure applied torque and angular motion; and measuring torque applied to the fastener at a plurality of sensed angular positions to obtain a plurality of torque-angle data points, the method being characterised by: determining a base slope for at least one of the plurality of torque-angle data points, wherein the base slope comprises a change in torque over a change in angle for the at least one torque-angle data point as compared to a base point; determining a forward slope for the at least one torque-data point, wherein the forward slope comprises a change in torque over a change in angle for a point subsequent the at least one torque-angle data point and the at least one torque-angle data point; determining a slope delta for the at least one torque-angle data point, wherein the slope delta comprises a rate of change between the forward slope and the base slope; and comparing the slope delta of the at least one torque-angle data point to a minimum slope delta, thereby obtaining an indication of a rate of change of torque per unit of angular motion of the at least one torque-angle data point as compared to the plurality of torque-angle data points. determining a base slope for at least one of the plurality of torque-angle data points, wherein the base slope comprises a change in torque over a change in angle for the at least one torque-angle data point as compared to a base point; determining a forward slope for the at least one torque-data point, wherein the forward slope comprises a change in torque over a change in angle for a point subsequent the at least one torque-angle data point and the at least one torque-angle data point; determining a slope delta for the at least one torque-angle data point, wherein the slope delta comprises a rate of change between the forward slope and the base slope; and comparing the slope delta of the at least one torque-angle data point to a minimum slope delta, thereby obtaining an indication of a rate of change of torque per unit of angular motion of the at least one torque-angle data point as compared to the plurality of torque-angle data points.