Abstract: For the automatic checking of the operational accuracy of inspection machines used in a bottle inspection operation, a star wheel with angularly spaced pockets for the bottles is rotated past testing heads. One or more checking parts are positioned relative to the star wheel to provide an automatic check of the accuracy of the inspection afforded by the testing heads. The checking operation can be effected without interrupting the inspection procedure. The checking can be performed continuously or at specific intervals. Accordingly, a continuous check can be kept on the inspection procedure, in particular without the use of test bottles.