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The 12-hour clock is a time convention in which the 24 hours of the day are divided into two periods: ... The first mechanical clocks in the 14th century, ...
An Egyptian method of determining the time during the night, used from at least 600 BC, was a type of plumb-line called a merkhet. A north–south meridian was created using two merkhets aligned with Polaris, the north pole star. The time was determined by observing particular stars as they crossed the meridian. [24]
The mechanical kitchen timer was invented in 1926. The simplest and oldest type of mechanical timer is the hourglass - which is also known as "the glass of the hour" - in which a fixed amount of sand drains through a narrow opening from one chamber to another to measure a time interval.
The timer may switch equipment on, off, or both, at a preset time or times, after a preset interval, or cyclically. A countdown time switch switches power, usually off, after a preset time. A cyclical timer switches equipment both on and off at preset times over a period, then repeats the cycle; the period is usually 24 hours or 7 days.
Since then, kè has been used as shorthand to talk about time in 1 ⁄ 8 of a double hour or 1 ⁄ 4 of a single hour. Their usage is similar to using "quarter hour" for 15 minutes or "half an hour" for 30 minutes in English. For example, 6:45 can be written as "6 diÇŽn, 3 kè" (å…点 三 刻; å…點 三 刻). MiÇŽo is now the standard term ...
In the current design, a slow mechanical oscillator, based on a torsional pendulum, keeps time inaccurately, but reliably. At noon, the light from the Sun, a timer that is accurate but (due to weather) unreliable, is concentrated on a segment of metal through a lens. The metal buckles and the buckling force resets the clock to noon.
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