What is the horizontal general binding line of A4 paper?

The transverse binding line of A4 paper is 250mm \ x0d \ x0d \ A4 paper is defined by ISO 2 16, and its specification is 21* 29.7 cm (210 mm× 297 mm), which is the paper size used by most countries in the world. This standard was first compiled into DIN (DIN 476) by the German Empire in 1922. Although some of its formats were formulated by France at the same time, they were later forgotten. ф o 216defines three groups of paper sizes: a, b and c: Group C paper size is mainly used for envelopes. \ x0d \ The aspect ratio of the paper size is √ 2: 1, and then the nearest millimeter value is rounded. A0 is defined as paper with an area of one square meter and an aspect ratio of √ 2: 1. The following paper sizes, such as A 1, A2, A3, are all defined as the paper with one digit missing is folded in half along the long side, and then rounded to the nearest millimeter. The size of group B paper is the geometric average of the same number of sheets and one less number of sheets of group A paper. Group C paper size is mainly used for envelopes. \x0d\ Chinese national standard GB/T 148- 1997 "Paper size for printing, writing and drawing" is not equivalent to ISO2 16: 1975.