[en] Results of measurements of the mean energy of protons in the beam extracted from the LINF synchrocyclotron are presented. The beam mean energy was determined by the Cherenkov method of double reflections. The obtained results are compared with the beam energy determined by a different method. It is demonstrated that the Cherenkov instrument for measuring the energy of protons in a beam by the method of double reflections allows one to determine the mean beam energy in the vicinity of 1 GeV with relative accuracy not worse than 0.1%