This part of IEC 60953 establishes a Supplementary Standard (SS) for thermal verification tests of retrofitted steam turbines. The rules given in this SS follow the guidance given in IEC 60953-0, hereinafter called the Reference Standard (RS) but contain amendments and supplements regarding guarantees and verification of the guarantees by thermal acceptance tests on retrofitted steam turbines. General principles for the preparation, performance, evaluation, comparison with guaranteed values and the determination of the measurement uncertainties of verification tests are given in this SS. This SS is applicable only when the retrofit involves some hardware change in the steam turbine equipment. Conversely, any modification on the cycle or any retrofit of other equipment of the power plant (e.g. boiler, feedwater heaters, etc.) is not covered by this SS.