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An hourglass (or sandglass, sand timer, or sand clock) is a device used to measure the passage of time. It comprises two glass bulbs connected vertically by a narrow neck that allows a regulated flow of a substance (historically sand ) from the upper bulb to the lower one due to gravity .
The equation of time was engraved on sundials so that clocks could be set using the Sun. In 1720, Joseph Williamson claimed to have invented a clock that showed solar time, fitted with a cam and differential gearing, so that the clock indicated true solar time. [137] [138] [139]
[2] [3] Filled with the amount of sand suitable for measuring a lapse of half an hour, each time the sand emptied was also called a "glass"; eight glasses (four hours) defined a "watch". [ 2 ] [ 3 ] The times determined by the sandglass, along with the record in the logbook of the speed measured with the " chip log ", permitted the ship's ...
In 1802 Madras Time was set up by John Goldingham [7] and this was later used widely by the railways in India. [8] Local time zones were also set up in the important cities of Bombay and Calcutta and as Madras time was intermediate to these, it was one of the early contenders for an Indian standard time zone.
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Whether the 24-hour clock, 12-hour clock, or 6-hour clock is used. Whether the minutes (or fraction of an hour) after the previous hour or until the following hour is used in spoken language. The punctuation used to separate elements in all-numeric dates and times .
Swatch Internet Time (or .beat time) is a decimal time system introduced in 1998 by the Swatch corporation as part of the marketing campaign for their line of ".beat" watches. Those without a watch could use the Internet to view the current time on the watchmaker's website, but now a dedicated wiki serves the purpose. [ 1 ]
The next 3 decades saw the development of quartz clocks as precision time standards in laboratory settings; the bulky delicate counting electronics, built with vacuum tubes, limited their use elsewhere. In 1932 a quartz clock was able to measure tiny variations in the rotation rate of the Earth over periods as short as a few weeks. [39]