[en] Results of state testing of the crystalline maximum temperature meter (CMTM) have been presented. The root-mean-square error of a separate measurement under stationary and nonstationary conditions constitutes 6 and 12 deg, respectively. Comparison of statistical data with the data obtained by means of the CMTM permitted to obtain measurement equations excluding a part of the error systematic component. Dependences of the root-mean-square deviation (RMSD) on the measured temperature level are obtained both for the diamond and silicon carbide CMTM. RMSD dependence on the temperature has been also estimated by the calculation method based on common considerations. The minimum RMSD value (about 4-5 deg C) is found to be achieved in the 500-1000 deg C temperature range. Brief description of other methods of temperature measurement in a complicated areas for measurements of technical installations is presented and RMSD dependences on measured temperature are considered