Second, the occupation formula table:

399 multiplication table:

Extended data:

Features of Jiujiu Watch:

General 1 and 99 tables only use 9 numbers from 1 to 9.

2. Jiujiu table contains the commutativity of multiplication, so only 8972 is needed, and "9872" is not needed. 9 times 9 has 8 1 product, and the 99 table only needs 1+2+3+4+5+6+7+8+9 =45 product. In the Ming Dynasty, abacus also had 99 tables with 8 1 product. The 99 table of 45 items is called small 99, and the 99 table of 8 1 item is called big 99.

3. The shortest multiplication table in the ancient world. Maya multiplication table must have 190, Babylon multiplication table must have 1770, and Egypt, Greece, Rome, India and other countries must have infinite multiplication tables; However, table 99 only needs 45/8 1 item.

4. There is rhythm when reading aloud, which is convenient for memorizing the whole table.

5. Jiujiu watches have existed for at least 3000 years. It was used for calculation from the Spring and Autumn Period and the Warring States Period, and was improved and used for abacus in the Ming Dynasty. Now, the 99 standard is also the basic skill of elementary school arithmetic. Nowadays, people generally describe those who are scheming, calculating and planning as "having a career in mind".