the mean load variation in time bg dp dt according to equation 2 the mean metal temperature variation in time gmz dtm dt set at the analog value transmitter 10 and permissible at 300 u00b0 c is divided in the dividing circuit 11 by the metal temperature difference tdel to be traversed during start up rated at the temperature dependence of the material constants of the probe or respectively of the component reproduced thereby the temperature dependence is taken into account by the expression 1 atm u00d7 tk the combined mean temperature coefficient tk of the heat propagation set at the analog value transmitter 12 is multiplied in the multiplier circuit 13 by the deviation atm of the mean value of the mean metal temperature from the reference temperature 300 u00b0 observed during the entire starting up process in the adder circuit 14 is added further the quantity 34 1 34 the output signal a 14 is thus 1 atm u00d7 tk this quantity is multiplied in the multiplier circuit 15 by tdel as described above the output signal a 15 is applied to an input of the divider circuit 11 to yield the mean load variation bg as has been noted tdel is the metal temperature interval traversed during start up this quantity is formed in the combining circuit 16 from the steam end temperature tfe set at the analog value transmitter 17 less the temperature difference tdmn to steam to metal full load the temperature drop ta between.