The bandwidth-time product is used in calculating the confidence limit of a measurement. Confidence limits describe the uncertainty in measuring the level of random signals in finite periods of time.
For broadband random signals the standard deviation can be estimated by:
where
σ = standard deviation [dB]
B = bandwidth of the signal [Hz]
T = measurement time [s]
This shows that as the analysis bandwidth decreases so the measurement time must be increased to maintain the same standard deviation.
