In principle one pulse suffices. It is not possible to obtain a better velocity measurement corresponding to just a fraction of a revolution. The instrument averages over one full revolution, which will then be the resolution. For each revolution a column of air with a fixed length \(\mathit\ell\) passes through the rotor. This length is called the calibration length. Summing all these columns of length \(\mathit\ell\) over a particular period, often 10 minutes, we obtain the mean-wind speed in this period. For practical purposes we have chosen 2 pulses for each revolution, but it is really overkill.