A tide table, sometimes called a tide chart, is used for tidal prediction and shows the daily times and height of high water and low water for a particular location. Tide heights at intermediate times (between high and low water) can be approximately calculated using the rule of twelfths or more accurately by using a published tidal curve for the location.
Tide tables are published as small booklets in their own right, as part of nautical almanacs, on the Internet, in some newspapers (generally those serving readers in coastal regions or having maritime interests) and as the output of tidal prediction software.
Tide tables are only calculated and published for major commercial ports called standard ports. The tides for nearby minor ports can be estimated by time and height differences between a "standard" port and these minor ports.
The dates of spring tides and neap tides, approximately seven days apart, can be determined by the heights of the tides on the tide table: a small range indicates neaps and large indicates springs.
On the Atlantic coast of northwest Europe, the interval between each low and high tide averages about 6 hours and 10 minutes, giving two high tides and two low tides each day.
Tide prediction was long beset by the problem of laborious calculations; and in earlier times, before the use of digital computers, official tide tables were often generated by the use of a special-purpose calculating machine, the tide-predicting machine.