Relative fluctuations of an extensive observable
= Relative fluctuations of an extensive observable
{title2=$\sqrt{\operatorname{Var}(A)}/|\langle A\rangle|=O(N^{-1/2})$}
If a total observable has a nonzero extensive mean and its variance is proportional to particle number, its relative standard deviation falls as $N^{-1/2}$. Short-ranged correlations away from a critical point often justify this scaling. A vanishing mean, a shifted energy reference or anomalously large correlations requires separate treatment.