In the international system of units, the basic unit of mathematics, the standard unit of length is "meter", which is represented by the symbol "m". 1960 The 1st International Metrology Conference: "The length of the meter is equal to 1650763.73 times of the radiation wavelength passing between 2P 10 and 5d 1 levels of krypton -86 atoms in vacuum".
Starting from 1983, the length of meter is defined as "the distance that light travels in vacuum in 1/299792458 seconds". The unit of length adopted in China is consistent with the international system of units, that is, "meter" is the legal unit of length measurement in China.
When measuring the length of a line segment:
You need to select a line segment as the measurement standard and specify its length as 1, which is called the length unit. There are many units in length, the main unit is meter, and the rest are derived units. When measuring, choose the appropriate length unit according to the actual needs. For example, the length of the runway is in meters, the distance between two cities is in kilometers, and the distance of long jump is in centimeters.
To understand the unit of length, we must first understand its superordinate concept-unit. The definition of "unit" in Modern Chinese Dictionary is: the name of the standard quantity to measure things. In measurement, a certain kind of quantity is taken as a reference quantity to determine how many times the known quantity is equivalent to the reference quantity, which is called a unit.
For example, centimeter is the unit for measuring length, gram is the unit for measuring mass, and second is the unit for measuring time. As an example of mathematics, it can also be said that 1 is the unit of natural number, and the fraction with the numerator of 1 is the unit of fraction.