Editing Allan variance (section)

==Linear response==
While Allan variance is intended to be used to distinguish noise forms, it will depend on some but not all linear responses to time. They are given in the table:
:{| class="wikitable"
|+ Allan variance linear response
|-
! Linear effect
! time response
! frequency response
! Allan variance
! Allan deviation
|-
| phase offset
| <math>x_0</math>
| <math>0</math>
| <math>0</math>
| <math>0</math>
|-
| frequency offset
| <math>y_0t</math>
| <math>y_0</math>
| <math>0</math>
| <math>0</math>
|-
| linear drift
| <math>\frac{Dt^2}{2}</math>
| <math>Dt</math>
| <math>\frac{D^2\tau^2}{2}</math>
| <math>\frac{D\tau}{\sqrt{2}}</math>
|}

Thus, linear drift will contribute to output result. When measuring a real system, the linear drift or other drift mechanism may need to be estimated and removed from the time-series prior to calculating the Allan variance.<ref name=Bregni2002/>