The temperature coefficient of capacitance of a metallized-mica capacitor varies with frequency as a result of relaxation processes, and is therefore correlated with the power factor of the mica. The temperature coefficient of commercial capacitors ranges at least from −40 to +100 parts in a million per degree centigrade at 1 kc/s; it may be more negative, by about 40 parts in a million per degree centigrade, at 1 Mc/s. There is usually a non-cyclic variation as well, which may be of the order of 0.1%.