Slide 13 of 59
Notes:
On short timescales, the order of a few days or so, the slowing down of the pulsar’s spin rate is remarkably uniform.
On longer timescales however, irregularities of the pulse timing become apparent. These are observed once every few years in the Crab and Vela pulsars, for example. The most studied of these are the so-called ‘glitches’ in pulse arrival time. These are discontinuous changes of period, ie ‘steps’ in the pulse arrival time distribution.
See Smith p60-61, Longair p104