A changing station for sleeves of a printing machine has a conveyable magazine with at least one take-up device for the sleeves. The method also includes iteratively modifying at least one of the pluralities of thermal cycle parameters so the glass strain is not greater than the set glass strain level after a final thermal cycle is completed. Periodically, detection of the duty cycle output from the duty cycle correction circuitry 26, 28, 30 is performed to determine whether or not this has drifted outside of a threshold range of duty cycles and if necessary the digital correction value is changed to bring the duty cycle back within the threshold range.