Construction of the waterfall-PCA folding merit function _ξ^ℓ (3) for M = 200 for the Crab pulsar observation. The plot shows three curves, the maximum scalar (1), the eigenvalue corresponding to the same _sℓt,max (high signal-to-noise ratio case corresponds to the first PC eigenvalue), and the merit function _ξℓ The strength in signal-to-noise ratio for an ideal pulsar observation is clear. The scalar, very low with respect to the rest (with 1 the maximum amplitude) of the curves, is plotted in Fig. 8. Eigenvalues from the same dataset are shown in Fig. 6.