The MS 422 is an optional selector device for the Marble MS421B bridge nautical watch alarm system. This device is used to select which backup officer is to be alarmed in case of emergency situations when the watch alarm enters the â€œcall officerâ€ stage. This situation occurs when the officer on the bridge canâ€™t respond to the signalling watch alarm. The six yellow ledâ€™s indicate which backup officer is to be ordered on the bridge during emergency situations. Use the rotary switch at the panel change backup officer. A maximum of six backup officers can be selected.