Each Clock is a large 9" in diameter Choice of White or Black Plastic Frame with a Glass Cover Perfect for beachcombers, fishermen, surfers, swimmers and boat owners! Tide Clocks are useful and exciting additions to any coastal home, offering a simple and reliable way to tell the time of the local tides. The tides run on moon time, where each day has 24 hours and 50 minutes, so high and low tides do not occur at the same hour each day. Most places have two high tides and two low tides each day. Our Tide clocks have been designed so that the hand rotates once every 12 hours and 25 minutes (twice each lunar day) Your Tide clock is always stays in step with the moon. Our Tide Clocks work best along the Atlantic Coast. Tide Clocks do not operate in the coastal areas of the Gulf of Mexico. Personalized Tide Clock. Makes a great gift! Perfect for beachcombers, fishermen, surfers, swimmers and boat owners!.