In tempo/tempo2, glitch events are modelled as an offset in pulse phase, and the permanent increments in the pulse frequency and first frequency time derivative . In addition it is sometimes necessary to in a transient frequency increment which decays exponentially to zero with a timescale of . The phase model (caused by the glitch) is therefore taken as:
where is the glitch epoch and is the current time.
Frequency-dependent and frequency-independent noise