Time comparison

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A time comparison or clock comparison is the comparison of the time information of a clock with a time signal (radio signal) of a more precise time system or the comparison of two clocks with each other.

The design of the clock is irrelevant. It can be: a wristwatch , a stopwatch , a grandfather or pocket watch , a pendulum watch , a digital stopwatch , a chronometer or a chronograph . High-precision quartz watches and even atomic clocks are checked against each other or with radio signals.

With more precise clocks, time or clock comparisons are cheaper than readjusting the clock, because they do not cause any interference from mechanical or electronic interference. With simple displays such as on cell phones or digital cameras, however, setting the time has no disadvantages, but you have to reckon with a delay of about ½ second.

Clock and time comparisons are particularly necessary

  • to determine the status of the so-called work clock
  • for quality control of the watch (uniform movement , temperature influences, etc.)
  • for the mutual control and comparison of international time services .

Process of time comparison

A time or clock comparison is made by determining the display of the clock relative to the comparison signal ( master clock , chronograph, time signal) at a clearly defined moment . This point in time can be arbitrary, but is usually a signal triggered by the observer, which is generated manually, optically-audibly, electronically, on the chronograph, with a coincidence signal or by triggering . The comparison can also be made by electrical time registration of both signals or clocks, with which milliseconds can be achieved.

One of the simplest methods is the eye-to-ear method , which achieves an accuracy of at least 0.05 seconds when clocks are ticking exactly. Between the 18th and the middle of the 20th century it was one of the standard methods of astrometry and is e.g. Till today in length determinations in navigation and visual astrogeodesy .

An absolute time comparison refers to the internationally coordinated world time UTC or the atomic time correlated with it . However, the UT1 time scale is relevant for astronomical observations . It differs from UTC by a small time correction dUT1 , because the earth's rotation has irregularities in the range of tenths of a second . Relative time comparisons can refer to approximated time scales or consist of a simple comparison of two clocks.

The difference between the work clock used for a measurement and the target value (usually the radio signal from a time signal transmitter ) is known as the "clock status". Its sign is defined in terms of improving the reading of the clock. The slow change of the clock position is called clock rate (deviation from the uniform course of time) and is v. a. caused by temperature changes, voltage or position changes and any shocks.

Since the development of digital stopwatches , a manual time comparison can achieve an accuracy of a few milliseconds if the switching noises of the watch coincide acoustically with the time signal (radio or telephone). Electronically, about microseconds can be achieved with quartz watches, and with atomic clocks, time differences of up to 10 −14 can be proven with great effort .

See also

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