The frequency at which a data set is sampled is determined by the number of sampling points per unit distance or unit time, and the sampling frequency is equal to the number of samples (or stations) divided by the record (or traverse) length. For example, if a wave-form is sampled 1000 times in one second the sampling frequency is 1k Hz (and the Nyquist frequency 500 Hz); if a traverse is 500 m long with 50 stations, the sampling frequency is one per 10 m.