钟(clock)
一种计算和记录时间的机械或电子装置。机械钟包含一种相等时距内作有规律运动的装置及与之相联动的将运动次数记录下来的计数机件的机器。第一座时钟可能是由修道院发明使用的。欧洲第一座公用打点的时钟是在米兰建造的（1335）。现存最古老的时钟保存在英格兰（1386）和法国（1389）。最早的家庭时钟出现在14世纪後期。约1500年德国锁匠亨莱恩（P. Henlein, 1480～1542）开始制造由弹簧控制、第一次可携带的小时钟。惠更斯在1656年发明钟摆。1859年在威斯敏斯特安装了大班钟，该钟成为所有精确塔钟之标准。最准确的机械计时器（每天误差在千分之几秒以内）是短钟摆（摆长约为99公分）的时钟。1929年石英晶体首先应用於计时，天文台石英钟最大误差每天不过万分之几秒。1951年第一座原子钟开始运作，这是一种利用原子的某种共振频率使时间保持特殊精准度的计时器，其准确度每天只超出十亿分之一秒，成为目前最精准的时钟。
English version：
clock
Machine or electronic device that measures and records time. A mechanical clock consists of a device that performs regular movements in equal intervals of time, and is linked to a counting mechanism that records the number of movements. The first clocks may have been invented for use in monasteries. The first European public clock that struck the hours was erected in Milan in 1335. The oldest surviving clocks are in England (1386) and France (1389). The first domestic clocks appeared late in the 14th century. About 1500 Peter Henlein, a German locksmith (1480-1542), began to make the first portable timepieces, small clocks driven by a spring. Christiaan Huygens invented pendulum clocks in 1656. Big Ben, the great clock at Westminster in London, was installed in 1859 and is the standard for all accurate tower pendulum clocks. The most accurate mechanical timekeepers (within a few thousandths of a second per day) are clocks with short pendulums (about 39 in., or 990 mm). In 1929 the vibration of a quartz crystal was first applied to timekeeping; the maximum error of an observatory quartz-crystal clock is only a few ten-thousandths of a second per day. The first atomic clock went into operation in 1951. Atomic clocks, regulated by the natural periodic behavior of a system of atoms (such as vibrations or emission of radiation), can have accuracies exceeding one billionth of a second per day, making them the most accurate clocks yet invented.