Abstract: An apparatus and method for determining variations in a dimension of a structural member caused by compressive or tensile forces acting on said member. The apparatus comprises an elongate member secured at or adjacent one end to said structural member and extending in the direction in which the variation is to be measured, and a position detector secured to the structural member adjacent the free end of the elongate member, the linear coefficient of thermal expansion of the elongate member and the structural member in said direction being equal and the arrangement being such that, in use, when the force acting on said structural member in said direction changes, the position detector (which is preferably a linear differential transformer) transmits a signal which is a function of the change in distance between the free end of said elongate member and said position detector.A device is also disclosed which comprises an apparatus as described above in combination with a visual display meter.