The impulse weighting is the same as the impulse response in a sound level meter and is part of the rms. circuit controlling the response of the meter to the variability of the instantaneous levels of the noise. It has a rise time value of 35 milli seconds and a decay time of 1500 milli seconds. The asymmetric nature of the impulse weighting means that any average sound level calculated based on samples of the instantaneous will be biased towards the higher noise events than will the average calculated from either the fast or slow response. It is a continuous function that is calculated all the time by the instrument.