Examples of the present disclosure relate to a calibration method for a printing system. The method comprises printing a diagnostic pattern representative of decap time. The diagnostic pattern comprises the firing of nozzles after an exposure to ambient air during a first predetermined time period to produce a first pattern element and the firing of nozzles after an exposure to ambient air during a second predetermined time period to produce a second pattern element. The method includes scanning the resulting diagnostic pattern with a sensor to collect decap data in a digital form, digitally analyzing the decap data, the digital analysis comprising identifying a quantitative difference between the first and second pattern elements, and modifying a servicing process of the printing system if the quantitative difference passes a predetermined threshold.