Example of pulse sequences in the Q and B modes from the observing session L102418. Only the on-pulse longitude region is shown. In the B mode the apparent drift period is similar to two rotation periods, which results in the distinct even-odd modulation of the subpulses (see Sect. 6 for the discussion of the sign). If were exactly 2P₁, drifting subpulses would appear at the same longitudes during every other rotation period. Because is slightly larger than 2P₁, however, thesubpulses appear to be slowly shifting towards the leading edge of the average profile, with an apparent cycle of about 10P₁.