Abstract: In trimming a constituent layer (10) of a circuit element, through which layer current is to flow along an axis (14), a first channel (16), extending through the layer from one layer edge, (17), partially across the width of the layer, transversely to the axis, is provided in a first, coarsest trimming action, a second channel (18), extending through the layer, from the extremity of the first channel remote from the layer edge, parallel to the axis, is provided in a second finer, trimming action, and in each of at least one further trimming action a further channel (20) is provided, each further channel extending through the layer parallel to the axis, the further channels being successively between the immediately previously provided channel and the layer edge, there being successively greater accuracies associated with the constituent trimming actions, each further channel possibly extending further from the first channel than the immediately previously provided channel.