The invention relates to a method for determining the amplitude A of pseudo-sinusoidal deformations of a structural element area consisting in placing in said area at least two stress gauges (1) each of which produces a signal VI based on the deformation thereof, in forming at least two signals SI according to variations of at least one signal VI emitted by the gauges (1) during deformation, in forming two SIN and COS signals based on the signals SI for the same angle and the same A-dependent amplitude, and in calculating a SIN2 + COS2 expression in such a way that the amplitude A is derived therefrom. A system for determining by means of the inventive method is also disclosed.