"7" is like a hoe: draw a horizontal line from the upper left corner to the upper right corner, then fold the line downward, and touch the line to the left of the middle of the bottom line.

During the printing process, because "7" is similar to the printed "1", a horizontal line is added to distinguish the two numbers.

In accounting, in order to prevent tampering with numbers, a horizontal line should be added in the middle when writing "7".

Extended information:

Historical origin:

Roman numerals are more than 2,000 years earlier than Arabic numerals and originated in ancient Rome.

The most commonly used way of expressing 4 by the ancient Romans was IIII, so the design style of IV has always been strongly protested by "orthodoxists". James O'Donnell, professor of classical literature and provost at Georgetown University, said that although the ancient Romans sometimes wrote 4 as IV to save space, this abbreviation did not become popular until the Middle Ages. In fact, this writing is not formal. .

Some clock experts also put forward a theory: the ancient Romans used IV as the abbreviation of the name of Jupiter, the king of the gods (in classical Latin, J and I are both I, U and V are both V, Therefore IV is JU, short for Jupiter).