Quasistationary noise in resistors

Carbon resistors, operated at very low currents, showed a quasistationary noise spectrum at very low frequencies. Over long periods the stationary noise power density followed S(¿) = K¿¿ß, with ß close to unity. Then sudden large fluctuations occurred ending in another stationary period, but K may have changed its value. This behaviour explains a difficulty in repeating l.f. noise measurements.