Each year the United States Coast and Geodetic Survey issues four paper-covered books containing information about the rise and fall of the tide at about six thousand places in various parts of the world. Every ship carries official tide tables. They also carry a nautical map that includes the level of the water in certain plaes, at lowest tide. With these two maps, one can figure out when low tide is by the tide tables, and how low the tide is by the nautical map, this way they know when the best time to sail into a port is without grounding their boat. On a tide table information is included to help calculate close to exact times the tide will be at a specific hieght. The first official tide table was issued bythe Brittish Admiralty in 1833. The United States began to compile tidal information in 1853. The easiest and least complicated instrument to use today is a long ruler called a tide staff. It is marked off into feet, and each foot is subdivided into tenths. To use this instrument one must first fasten it to a bulkhead, or piling, and record the location for the acurate collectiong of further data. Then the tide must be recorded at periodic intervals, a ood interval is every fifteen minutes to every half hour. Now they have an automatic tide gauge which draws a continuous picture or graph of the rise and fall of the tide. This is run by clocks which last eight days before they are needed to be winded. Normaly a daily check is made, just to make sure, and recored any useful data. That is bascilly how the machim\ne works. After about a month, the graphs are taken out, information is recorded into specific areas, everything is compiled, numbers are tabulated, and scientists go to work. Also, skillful mathematicians are needed to compute certain data.
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