Abstract: A ball controller (10) is in the form of a rigid mat having a central cavity (12) for the reception of a golf ball (11) for checking the diameter of a golf ball (11), the ball controller (10) having sectionally (13, 14, 15) differing wall thicknesses (a, b, c) in the radial direction of the controller (10) and preferably having an optimal thickness in a radially innermost, annular portion (15) around the cavity (12). The cavity (12) has a cylindrical inner face (14a) having an axial dimension (1) of 3 mm minimum.