Determining the thicknesses of one or more layers (1,4) on a substrate (2), where at least one layer or the substrate is electrically conductive, comprises measuring the disturbance on an imposed variable magnetic field (8) of the eddy currents (9) excited in the conductive layer (2). Measurements are taken for at least two different frequencies of imposed magnetic field, and the layer thickness is calculated based on data from previous measurements and at least some of the electromagnetic properties of the substrate and the layer or layers. Also claimed is a device for carrying out the above process.
