It is an object of the present invention to provide a high-quality printed image in a printing machine. To achieve this, a method for adjusting a fusing device 100 of a digital printing machine has been provided, in which case microwave signals of a specific frequency or frequency range are directed at a printing material 5, a change between the microwave signals reflected by the printing material and the emitted microwave signals is detected, and in which case the fusing device is adjusted based on the change between said microwave signals. Furthermore, a measuring device 20 for a printing machine is provided, said device preferably being used for carrying out the said method, whereby the measuring device is configured so as to detect a change between a microwave signal reflected by the printing material 5 and a microwave signal directed at said printing material.