Energy calibration of the NaI(Tl) calorimeter of the SND detector using $e^+e^- to e^+e^-$ events

Calibration of the three layer NaI(Tl) spherical calorimeter of the SND detector using electron -- positron scattering events is described. Energy resolution of $5 % (FWHM/2.36)$ for 500 MeV photons was achieved.