First it is demonstrated that through stepwise pergression of a constant analysing interval p throughout a sine the period T can be calculated even if p is not an integer multiple of T. The key is the fact that the two harmonics n=n1=[r] and n= n2=[r]+l produce parallel regression lines in the phase diagram with the standardized slope r=p:T. Through an iterated second analysis with an integer multiple of T as analysing interval the three sine parameters can be accurately calculated with the aid of the amplitude and phase diagrams. But it is also demonstrated that often the iteration of the analysis can be avoided.