Waterfall diagram of a two-hour Crab pulsar acquisition OBS2 (Table 1). The two columns have the same datasets, same number of divisions (M = 200), and time bin (∆t = 10 µs), but different trial periods P_t. Left column: P_t = 33.637 20 ms, and the right column has P_t = 33.637 26 ms, i.e., a difference of 60 ns. Top panels: average along the m-axis (number of divisions or number of light curves, of each waterfall matrix . Vertical straight lines appear only when the adopted period corresponds to the best estimate. In addition, a perfectly straight line may not be possible because we did not consider pulsar spin-down or other effects in this calculation.