A variable resistor having a multi-layer resistive/conductive element is provided. The resistor has three electrodes, a resistive element connecting two of the electrodes and a sliding contact between the resistive element and the third electrode. The base of the resistor is provided with test areas. Each of the test areas contains a strip of the material used to form an individual layer in the multi-layer element. The test areas provide a convenient means for measuring the thickness of the individual layers in the multi-layer element without having to destroy the resistor.
