A tide clock is a specially designed clock that keeps track of
the Moon's apparent motion around the Earth. Along many
coastlines the Moon contributes the major part (67 percent) of
the combined lunar and solar tides. Tide clocks keep an
approximation of the average time between high lunar tides: 12
hours 25 minutes per revolution. As the precise average time
between high lunar tides is actually half of a lunar day, or 12
hours 25 minutes 14 seconds, tide clocks gain about 15 minutes
per month and must be reset periodically. The bottom of the tide
clock dial is marked "low tide" and the top of the tide clock
dial is marked "high tide." The left side of the dial is marked
"hours until high tide" and has a count-down of hours from 5 to
1. There is one hand on the clock face, and along the left side
it points to the number of hours "until" the (lunar) high tide.
The right hand side of the clock is marked "hours until low
tide" and has a count-down of hours from 5 to 1. The number
pointed to by the hand gives the