The Nine-Nine Song is the multiplication formula we use now. As early as the Spring and Autumn Period and the Warring States Period before Christ, the Nine-Nine Song was already widely used by people. Many works at that time had records about the Nine-Nine Song. The original Nine-Nine Song was from "Nine Nines are Eighty-One" to "Two Twos are Four", with a total of 36 sentences. Because it started from "Nine Nines are Eighty-One", it was named the Nine-Nine Song. Around the fifth to tenth century AD, the Nine-Nine Song was expanded to "One One is One". Around the thirteenth and fourteenth centuries AD, the order of the Nine-Nine Song became the same as it is used now, from "One One is One" to "Nine Nines are Eighty-One". There are two types of multiplication formulas used in my country now, one is 45 sentences, usually called "small Nine-Nine"; the other is 81 sentences, usually called "big Nine-Nine".