Optical power meters usually display time-averaged power. So for pulse measurements, the signal must be known to calculate the peak power value. However, the instantaneous peak power must be less than the maximum meter reading, or the detector may saturate, resulting in wrong average readings. Also, at low pulse repetition rates, some meters with data or tone detection may produce improper or no readings. A class of "high power" meters has some type of optical attenuating element.