A time weighting defines how the exponential averaging in the level (RMS) detector is done. It defines how the fluctuating sound pressure variations are smoothed or averaged to allow useful readings. There are three different time constants (F, S and I) available in the detector of this sound level meter. The Nor150 can measure all three time constants simultaneously.
The Peak function is always available and senses the amplitude of the time signal.
Measurement standards often tell which time constant to use for special purposes.