Waterfall-PCA folding merit function, ξ_ℓ, for waterfalls with a different number of divisions, M = 3,4, 8,10, and 15. The signal- to-noise ratio is clearly improved when M is increased up to a certain value (for this case for M > 10, the signal is slightly degraded). The Vela pulsar data have the original number of counts. The second row from top to bottom corresponds to the same merit function as plotted in Fig. 14.