Beam energy spread measurement at the VEPP-4M Electron-Positron Collider

The VEPP-4M electron-positron collider is now operating with the KEDR detector for the experiment of precise measurement of tau-lepton mass. In this experiment, monitoring of beam energy spread is important to know the energy spread contribution into the total systematic error. Information about the energy spread gives an opportunity to reduce the error of the tau-lepton mass measurement. Several techniques for energy spread measurement are described in the paper. Width of the ψ' resonance measured with the KEDR detector is used as a reference