A measuring tool is a tool for measuring a certain property. Includes length, temperature, time, mass, force, current, voltage, resistance, sound, radio, refractive index and average dispersion.

Some mechanical measuring tools, such as squares, calipers, etc., were first used in mechanical manufacturing. In the 16th century, smooth gauges were used in artillery manufacture. In 1772 and 1805, British J. Watt and H. Maudsley, etc. successively produced a Watt micrometer and a calibration length measuring machine using the principle of thread pair. After the mid-19th century, measurement tools similar to modern mechanical outer micrometers and vernier calipers appeared successively. At the end of the 19th century, sets of gauge blocks appeared. Following the emergence of mechanical measuring tools is a group of optical measuring tools. At the end of the 19th century, vertical length measuring instruments appeared, and at the beginning of the 20th century, length measuring machines appeared. By the 1920s, projectors, tool microscopes, optical micrometers, etc. had been used for measurement in mechanical manufacturing. In 1928, the pneumatic gauge appeared, which is a measuring tool suitable for use in mass production. Electrical measuring tools appeared in the 1930s. Initially there were limit gauges and profilers made with inductive length sensors. In the late 1950s, coordinate measuring machines that displayed measurement results digitally appeared. In the mid-1960s, coordinate measuring machines with electronic computer-aided measurement were used in mechanical manufacturing. In the early 1970s, the computer digitally controlled gear measuring instrument appeared again. At this point, the measuring tool entered the stage of applying electronic computers.

There are two main types of stopwatches: mechanical and electronic, and electronic watches can be divided into two categories: three-button and four-button. Most physical education teachers use electronic stopwatches, and mechanical stopwatches have become history in many places. The electronic stopwatch is a kind of advanced electronic timer. The domestic electronic seconds generally use the oscillation frequency of the quartz oscillator as the time reference, and use a 6-digit liquid crystal digital display to display the time, which has the advantages of intuitive display, convenient reading and multiple functions. .

The electromagnetic dotting timer is a magnetoelectric structure. When the coil is supplied with an alternating current of 50 Hz, the alternating magnetic field generated by the coil magnetizes the vibrating piece (made of spring steel), and one end of the vibrating piece is located in the magnetic field of the permanent magnet. Since the magnetic pole of the vibrating piece changes continuously with the change of the current direction, under the action of the magnetic field of the permanent magnet, the vibrating piece will vibrate up and down. One end of the vibrating sheet is equipped with a needle, when the paper tape passes under the needle tip. Then a series of points are marked, and the corresponding time between adjacent points is 0.02 seconds. The time corresponding to 5 intervals is 0.1 second.