Fluorescence localization precision (${\sigma }_{\mathrm{loc}}$)

The precision of a fitted single-emitter position is distinct from its diffraction-broadened point spread function width. An ideal Gaussian function image of width $s$ with $N$ independent detected photons gives ${\sigma }_{\mathrm{loc}}\simeq s/\sqrt{N}$. Pixel size, background, model error, sample motion and drift limit practical performance; precision alone does not guarantee accuracy.^[ref]