The invention pertains to a device and procedure to regulate the bale length in a square baler. Sensors determine both the forward and backward movement of the crop bundle and transfer these measurements to an evaluation electronic. The evaluation electronic adds the measurements and triggers the tying process when the actual length value is reached. The procedure includes the steps of: sensing both the forward and backward movement of a crop bundle in a baling chamber; adding the measured forward and backward movements to determine an actual length value of the crop bundle; and triggering the tying device once a pre-set target actual length value is reached.