A round baler (12) comprises a baling chamber (16) and a press means (20) mounted therewithin. A first sensor (S1) is disposed within said baler (12) to determine a diameter change of a bale (15). A second sensor (S2) is configured to detect a speed of a drive shaft (14). The speed of the drive shaft (14) and the diameter change after each rotation of the bale (15) processed to determine a thickness (Th) of a layer of said crop material. The thickness (Th) is indicated in a display unit (22).
