Tide tables, sometimes called tide charts, are used for tidal prediction and show the daily times and heights of high water and low water, usually 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.
Publication and Scope
Tide tables are published in various forms, such as paper-based tables and tables available on the Internet. Most tide tables are calculated and published only for major ports, called "standard ports", and only for one year — standard ports can be relatively close together or distant hundreds of kilometers. The tide times for a minor port are estimated by the tide-table user manually calculating using the published time and height differences between a "standard" port and the minor port.
Dates and times
The dates of spring tides and neap tides, approximately seven days apart, can be determined by the heights of the tides on the classic tide tables: a small range indicates neaps and large indicates springs.
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.