Editing Allan variance (section)

===Linear drift===
Systematic effects on the signal is only partly cancelled. Phase and frequency offset is cancelled, but linear drift or other high-degree forms of polynomial phase curves will not be cancelled and thus form a measurement limitation. Curve fitting and removal of systematic offset could be employed. Often removal of linear drift can be sufficient. Use of linear-drift estimators such as the [[Hadamard variance]] could also be employed. A linear drift removal could be employed using a moment-based estimator.