The fourteen glitches observed during 33 years do not show the simple pattern expected from a relaxation oscillator .
They may however be regarded as three major events separated by about 12 years , the third being a group of smaller glitches .
There is a step increase in slowdown rate at each glitch , whose cumulative effect makes a significant contribution to the second differential \ddot { \nu } .
The braking index n has previously been evaluated only between glitches : the effect of the glitches is to reduce n from 2.51 to 2.45 .
This extra effect due to the glitches would be explained by an increase in dipole field at the fractional rate of 1.5 \times 10 ^ { -5 } per annum .