Abstract: A paperboard blank processing apparatus including a rotatably mounted processing head for operating upon successive paperboard blanks is disclosed. A paperboard blank registration sensor is provided upstream from the processing head for detecting a preprinted registration mark on a surface of an approaching paperboard blank. A controller is responsive to the registration sensor for determining whether the approaching paperboard blank is in proper registration with the rotary processing head. A registration correction window is defined by the controller and includes upper and lower limits defining upper and lower maximum correction values for bringing the angular position of the processing head into proper register with the linear position of the approaching paperboard blank. The controller further defines an averaging window containing the registration correction window wherein the registration correction window may be shifted within the averaging window in response to consistent registration errors.