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When the clock reaches the halfway point ("half-tide"), it then counts the hours up to high tide or low tide, as in "one hour until high or low tide". Generally, there is an adjustment knob on the back on the instrument which may be used to set the tide using official tide tables for a specific location at either high or low tide.
A tide dial, also known as a mass dial [2] or a scratch dial, [3] [4] is a sundial marked with the canonical hours rather than or in addition to the standard hours of daylight. Such sundials were particularly common between the 7th and 14th centuries in Europe , at which point they began to be replaced by mechanical clocks .
Tide tables, sometimes called tide charts, are used for tidal prediction and show the daily times and levels of high and low tides, usually for a particular location. [1] Tide heights at intermediate times (between high and low water) can be approximated by using the rule of twelfths or more accurately calculated by using a published tidal ...
The water stops rising, reaching a local maximum called high tide. Sea level falls over several hours, revealing the intertidal zone; ebb tide. Oscillating currents produced by tides are known as tidal streams or tidal currents. The moment that the tidal current ceases is called slack water or slack tide. The tide then reverses direction and is ...
Tide tables forecast the time of the next high water. [6] [7] The difference between these two times is the lunitidal interval. This value can be used to calibrate tide clock and wristwatches to allow for simple but crude tidal predictions. Unfortunately, the lunitidal intervals vary day-by-day even at a given location.
Graph showing relationships between the rule of twelfths (coloured bars), a sine wave (dashed blue curve) and a clockface, if high tide occurs at 12:00. The rule of twelfths is an approximation to a sine curve. It can be used as a rule of thumb for estimating a changing quantity where both the quantity and the steps are easily divisible by 12 ...
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The columns show the bearing of the tidal stream and its speed, in knots, at both spring tide and neap tide. The times on the table are related to the high water of the standard port displayed on the table. To calculate the rate at an intermediate tide between neap and spring, interpolation is required.