Ship Bell is used for signaling, keeping time and sounding alarms. Bells are very important part of a ship's routine and readiness.Before the advent of the chronometer, time at sea was measured by the trickle of sand through a half-hour glass. One of the ship's boys had the duty of watching the glass and turning it when the sand had run out. When he turned the glass, he struck the bell as a signal that he had performed this vital function. This age-old practice of sounding the bell on the hour and half hour still holds a place in the modern Navy. The sounding of a ship's bell can serve as a warning signal to other vessels in poor visibility and fog. In 1858, British naval regulations made this warning function mandatory. Today, maritime law requires all ships to carry an efficient bell. Early American ships adopted many of the practices and traditions of the British navy, including the use of bells. In 1798, Paul Revere cast a bell weighing 242 pounds for the frigate Constitution. The ship's bell can announce the presence of important persons. When the ship's captain, a flag officer, or other important person arrives or departs, watch standers make an announcement to the ship and ring the bell. This tradition extends to major naval command transitions, often held aboard vessels associated with the command.