Track the tide with Harbormaster, a precision east coast tide clock.  It makes it easy to track the tide at your favorite coastal location, regardless of where you are.  Powered by a single AA battery (included), Harbormaster tracks according to the average time between lunar high tides in the Atlantic Ocean (12 hrs, 25 min.). Fluctuations in conditions, location and the distance of the Moon from Earth can effect this average. However, over a lunar month, your Harbormaster tide clock will provide a practical indication of local tides.