In recent years, we can observe the development of the thermal diagnosis and operating control systems based on measuring techniques and mathematical modelling of processes improvement. Evaluation of the actual operating state is insufficient to make an optimal operating decisions. Thus, information about the influence of the operating parameters' deviations from the reference state on indicators describing energy consumption of the process (for example specific heat consumption or specific energy consumption) is also necessary. The paper presents methods for generation the information about the influence of the steam-water cycle operating parameters on specific heat consumption in a turbine's cycle. A mathematical model of steam-water cycle for a CHP (Cogeneration - also Combined Heat and Power) unit is being worked out. Methods for calculation of operating deviations with the application of correction curves and a mathematical model are described. Exemplary calculation results are presented.