Provided in one example is a printing system that has a printing zone with a platen (10), a drive, a suction force generator (18), a media advance sensor (26) to monitor movement of the medium through the printing zone in a medium advance direction, and a controller 28) to perform suction force calibration prior to printing. The suction force calibration includes controlling the drive to cause movement of the medium from an initial position at least partly through the printing zone while the suction force generator is controlled to generate at least one suction force level, determining a suction force level to be used during printing on the medium based on the output of the media advance sensor during the movement, and moving the medium back to the initial position.