History of tide gauges
(Click the figures to enlarge.)
Kelvin-type Kelvin type tide gauge
Kelvin type tide gauges, which were devised by an English physicist, Lord Kelvin, and produced in England, were the main gauges used to observe tides from 1891, when tide observation started in Japan, to 1979. The early gauges used pencils and springs, such as those used in pendulum clocks, and it was necessary to wind the springs everyday. The Geospatial Information Authority of Japan modified them into pen-writing and self-winding gauges.
The distinctive feature of this type of tide gauge is to set papers vertically. The paper was prone to damping and stretching since the recorder had no cover.

Fuess Type Fuess type tide gauge
Fuess type tide gauges, which were made in Japan, were in use from 1963. The gauges were frequently modified to produce Types III, IV and V. The gauges were used until 1992.
A feature of this type of gauge is to place the recording paper horizontally and to have covers over the recorders to prevent from damping. The early gauges, like Kelvin type tide gauges, required the springs to be wound everyday. Subsequent modified gauges were electric-powered.

GSI Type GSI type tide gauge
This type of tide guage was developed by the Geospatial Information Authority of Japan(GSI) and used from 1966 to 1991. The early gauges used pendulums, and were later modified to use electric-mechanism.
These gauges could record tidal levels continuously for one month. Therefore, the gauges were also called GSI long-term winding tide gauges.

personal computer type High accuracy automatic tide gauge(personal computer type)
High accuracy automatic tide gauges (personal computer type), which were jointly developed by the Geospatial Information Authority of Japan and a private company, have been used since 1985.
The measurements of tidal level are digitized every 30 seconds with rotary encoders and buffered in computers, and transmitted to the Geodetic Observation Center of the Geospatial Information Authority of Japan through telephone lines. These are the most widely used gauges now.

data logger type High resolution automatic tide gauge(data logger type)
The personal computer-type high resolution automatic tide gauges were modified into the data logger-type, which have been gradually installed at tidal stations since 1997.
This type of gauges use data loggers instead of computers to reduce computer troubles due to damp and salt damage. The data logger-type gauges can work stably for a long period of time.

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