Spin component variance
= Spin component variance
{title2=$\operatorname{Var}(S_\alpha)=\langle S_\alpha^2\rangle-\langle S_\alpha\rangle^2$}
The uncertainty of a <spin projection> is measured by its <variance>. In a maximally polarized <spin coherent state>, the longitudinal <variance> is zero and each transverse <variance> is $S/2$ in units $\hbar=1$. The transverse fluctuations do not imply finite <magnon> occupation in an isotropic ferromagnet's polarized vacuum.