Abstract: The invention relates to a method of capacitively measuring variations in the previously adjusted nominal distance between the facing surfaces of a color selection electrode and a display window of given nominal glass thickness of a color television display tube. In this method, the distance is determined by measuring the capacitance of a capacitor electrode is formed by the color selection electrode and a measuring electrode which is disposed on the outer surface of the window and is surrounded by a screening electrode. The outside dimensions of the screening electrode are chosen so that, capacitance variations due to variations in the thickness of in the window are negligible in comparison to capacitance variations due to variations in the previously adjusted nominal distance between the facing surfaces of the color selection electrode and the window. The invention also relates to a device for carrying out the method.