Its international unit is "meter" (symbol "m"), and commonly used units are millimeter (mm), centimeter (cm), decimeter (dm), kilometer (km), meter (m), micron (micron) and nanometer (nm). Length units play an important role in various fields.

1 ft = 10 ft; 1 ft = 10 inch; 1 inch = 10 points; 1 = 10%.

1 sheet ≈ 3.33m; 1 ft ≈3.33 decimeter; 1 inch ≈3.33 cm

The unit conversion of centimeters is as follows:1cm =10 mm = 0.1decimeter = 0.0 1 m = 0.0000 1 km.

Introduction of ruler

Ruler: Ch ěㄔㄜˇ. Ch ǐㄔˇㄔˇ knows Chinese characters. Wang Yan: "The cloth refers to the inch, the hand knows the ruler, and the elbow knows the search." . "Shuo Wen Jie Zi": "Ten inches is also. Human hands are very arterial. Ten inches is a ruler. Ruler, what about the ruler? You too. What do you know from the body to B. B. Weekly system, the measurement of inch, ruler, embarrassment, search, regularity and phlegm is based on the human body. " .

The ancients used their own bodies as a reference to measure. The earliest inscriptions on gold inscriptions were marked with "ruler" under the herringbone to show measurement. From B (jué) to a corpse. The corpse is a variant of human beings, with identification symbols. The two paradigms of corpse and B are superimposed. The body part used to identify the reference is the standard form of the ruler.