Here we apply an intuitive approach to an understanding of cup-anemometer dynamics and overspeeding. After a short historical presentation, the (somewhat unrealistic) Schrenk model and its consequences are discussed. It is shown how the wind-direction fluctuations always will cause a positive bias on the measured mean wind velocity i.e., the mean-velocity component in the direction of the wind. This bias is the so-called DP-error (data-processing error), the expression being coined by Paul MacCready who, in the early seventies, constructed the first man powered aircraft, Gossamer Condor. It is shown that the DP-error can be eliminated by using a wind vane together with the cup anemometer. This is supported by full-scale field measurements.