Disclosed is a data cartridge library system capable of using a data cartridge holder. A model structure is selected and one or more reference signal values are generated for input into the system. This value is used as the criterion in deciding whether or not the electric motor is turned off or reversed. A rotatable electrical contact cup connected to the ratchet makes or breaks contact with a fixed electrical terminal in the body. One of the portion and the retention clip is flexible and the other of the portion and the retention clip is rigid.