Online classroom timer

The timer clock is an instrument, a device for measuring and displaying the time and used to measure the duration or to an event or process and contributes to better planning of individual activities. He is one of the oldest human inventions. In ancient clocks every hour playing a beep or bell of the bell, which is repeated as many times as time.

timer clock satisfy natural needs of man to measure short time intervals.

The size of the timer clock is different today - from atomic clocks, watches to watches towers. They are driven by a variety of mechanisms - gravity, springs, electricity etc. and are governed by different devices, one of which is a pendulum.

The stopwatch is a type of clock, designed to measure short periods of time with high precision. Its name comes from Greek mythology, specifically the god of time Chronos. First used in marine navigation and marine chronometer is called. It defines longitude using stellar navigation. John Harrison was the first to achieve the desired precision of these devices.


The watch is one of the oldest human inventions. One of the first clocks used in antiquity sun. In its current form the timer clock(24-hour) is used from the 12th century.
timer clockat the Royal Observatory, Greenwich
Sundials


Primitive means of measuring time known from antiquity. For example, in ancient Egypt device, dating around 1500 BC the shape of a T-square, measured the time by the shadow it casts. "T" device is oriented to the east in the morning. At noon, the device is rotated so that it can cast a shadow, and in the evening.

Sundials use the stylus to overshadow marked signs are calibrated so as to indicate each hour. Sundials indicate local time.
Water clocks

The most accurate gauges of old time water clocks (also called klepsidra). One was found in the tomb of Egyptian pharaoh Amenhotep I (1525-1504 BC). They can take time, even at night, but have the drawback that they require human intervention to regulate water leakage. Greeks routinely recorded all astronomical observations as accurately as possible timing. Arab engineers made several improvements to the water timer clockin the Middle Ages.  In the 11th century the Chinese invented the first mechanical watch with a trigger mechanism.


The hourglass uses the flow of sand to the timing. Most are widely used in navigation. Thus Ferdinand Magellan used 18 of them to every ship in his circumnavigation of the world Travels (1522).  Aromatic sticks and candles are often used in churches all over the world for online timing. In monasteries in Europe during the Middle Ages using water and mechanical watches.  Great progress significantly improved precision marked devices invented by Galileo Galilei and especially Christiaan Huygens, who coined the clock.


Today most accurate devices for measuring and timing are atomic clocks that can keep you up to the second accuracy over millions of years. They are used to calibrate other clocks and other devices for timing. Since 1967, the International System of Units used for its unit of time - seconds the properties of cesium atoms. SI defines a second as the duration of 9,192,631,770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the cesium atom-133.

Today is also the Global Positioning System in accordance with NTP (Network Time Protocol) can be used to synchronize all systems associated with time.