The maximum demand indicator consists of a bimetallic spiral which is expanded by the heat caused by the current circulating in it, driving the pointer. A second spiral, mounted in the opposition, compensates the effect of the ambient temperature. The ammeter uses a moving-iron movement with silicone oil damping and pivot suspension with spring loaded jewel bearings for vibration and shock resistance. They combine a maximum demand meter and a moving iron ammeter in one instrument. Due to its long response time, short interval current peaks are not registered and the instrument indicates by a black pointer the mean of the r.m.s. current in a specified period of time (15 minutes). The maximum indication is registered by the position of the red pointer, dragged by the black one. By means of a sealable knob it is possible to resetthe red pointer to the position of the black one in order to make a new reading. Moreover, they use the moving iron ammeter for measuring the rms value of the current at any racy.