When designing a general book, it is related to the size of a large piece of paper: 31x 43 (78.74 cm x109.22 cm). This piece of paper is folded in half to become two (four pages) at a time, which is called folio. The size of a high school math book is 20.9 cm wide and 29.4 cm long, which is similar to A4.

In 20001year, the General Standard for Layout of Primary and Secondary School Textbooks issued by the General Administration of Quality Supervision, Inspection and Quarantine proposed to "upgrade" the basic layout of primary and secondary school textbooks from 16 to 16.

The standard size of high school textbooks is 16, that is, 2 1cm*29.7cm, which is generally smaller than it, but not larger than it. It's better to have a bigger schoolbag, which is looser. The smaller primary school math book should be 32 kais, which is b5.

As an international unit, the unit of length "meter" originated in France. 1970, the French Special Committee took a quarter of the meridian of the earth passing through Paris as the benchmark quantity of meters, which was approved the following year.

After that, a team from Dunkirk went to Barcelona for measurement, and then made a platinum pole of 1799, and set the distance between two sections of this platinum pole as 1 m, which is the origin of "archive meter".

Later, due to the serious deformation of the archive meter, in 1872, "Mibenyuan" made of platinum alloy was used as the length unit. Using rice prototype as the objective standard of rice will lead to many defects, such as material deformation leading to the decline of accuracy, and even humidity, temperature and natural loss will affect the accuracy.

Moreover, once the original rice equipment is damaged, replication will become very difficult. The development of isotope spectrum light source in 1950s solved this problem. Taking the wavelength of light wave as the benchmark of length unit, the disadvantages of rice cooker are well solved.

With the progress of science and technology and the development of the times, a new definition appeared at the 1983 international dose conference: 1 meter is the length of light propagating in a vacuum with 1/299792458 seconds. Through the combination of light speed and time, a new "Mibenyuan" has been formulated.