At its simplest watches are a division of labor and serve as a type of resource management. It is the system by which mariners continue the operation of a vessel in turns, thereby allowing each other to rest in intervals and avoid complete exhaustion. Watch standing also refers to the duties required of sailors; it refers to their jobs. Depending on the complexity of the operation and the size of the ship’s company (those onboard) a number of watches may be implemented. This may include a Navigational Watch, Engineering Watch, and Deck Watch, each with members having little overlap with one another and almost entirely separate duties. On the smallest of vessels there may only be a single mariner onboard; in which instance all departments and duties fall to him or her.