The unit of measurement refers to the scalar defined and adopted according to the convention, and any other similar quantity can be compared with it, so that the ratio of the two quantities can be expressed by a number. The unit of measurement has the name and symbol given according to the agreement. ?

The unit of measurement refers to the agreed definition and specific quantity, which is used to quantitatively express the size of the same quantity.

All kinds of physical quantities have their own units of measurement, and the number of selected substances displayed under specified conditions is the standard of basic units of measurement. The choice of basic quantity can be different in different periods and disciplines. For example, in physics, seven physical units, such as time, length, mass, temperature, current intensity, luminous intensity and the amount of matter, are taken as basic quantities. Their unit names are: second, meter? Kilogram, Kelvin, Ampere, Candeira, Molar.

Derived quantity

Other quantities derived from basic quantities according to relevant formulas are called derived quantities. The unit of export quantity is called export unit. For example, the unit of speed consists of length and time unit, which is expressed by "meter/second".

Combined unit

Units composed of units of other quantities are called combined units. For example, the unit of pressure (Pa) can be composed of the unit of force (N) and the unit of area (m 2), that is, n/m 2.

China's legal unit of measurement adopts the international system of units, and its internal uses include:

The basic unit of the international system of units

International system of units auxiliary unit

Derived units with special names in the international system of units

The legal unit of measurement in China can be used in the international system of units.

A unit in the form of a combination composed of the above units.

Decimal multiples and fractional units consisting of prefixes and above.

1, length measurement unit and rate:

Kilometers (kilometers), meters, decimeters, centimeters and millimeters.

1 km = 1 km 1 km = 1000 m

1 m = 10 decimeter 1 decimeter = 10 cm

1 cm = 10/0mm

2. Unit of measurement and rate of area:

Square kilometers, hectares, square meters, square decimeters, square centimeters

1 km2 = 100 hectare

1 km2 = 1000000 m2

1 ha = 1 10,000 m2

1 m2 = 100 square decimeter

1 square decimeter = 100 square centimeter

3. Volume measurement unit and rate:

Cubic meters, decimeters, centimeters, liters and milliliters.

1 m3 = 1000 cubic decimeter

1 cubic decimeter = 1000 cubic centimeter

1 cubic decimeter = 1 liter 1 cubic centimeter = 1 ml.

4, quality unit and grade:

Ton, kilogram, kilogram, gram

1 ton = 1000 kg

1 kg = 1 kg

1 kg =1000g

5. Time unit and rate:

Century, year, month, day, hour, minute and second.

1 century = 100 1 year =65438+ February.

1 day =24 hours 1 hour =60 minutes

1 min =60 seconds

(The months of 3 1 day are 1, 3, 5, 7, 8, 10, 65438+February, and the months of 30 days are April, June and September,165438+/kloc-0.