Tides are caused mainly by the moons gravitational pull on the ocean.The time it takes the moon to reappear at the same place in the sky each day is 24 hours and 50 minutes . Most areas in the world have two high tides and two low tides a day, so the tide clock has been specially designed to rotate twice each lunar day (every 12 hours and 25 minutes) giving you a quick and easy indication of high and low water. The Quartz tide clock will always stay synchronized to the moon.

There are other influences on sea levels that effect exact tide times. Therefore the tide clock should only ever be used as a guide, and is not intended for navigational use

	The suns own gravitational pull, when lined up with the moon (full moon and new moon) creates higher and lower tides. This can alter tide times by up to an hour.
	Changing atmospheric pressure.
	Strong on-shore and off-shore winds.
	Changing volume of river flows.