What is the reason for the two rows of black dots on the production date of car glass?

[VonVincent]

The number indicates the production year of the glass, representing the last digit. The small black dots represent the production month of the glass. If the black dots are in front of the number, subtract the number of dots from 7; if they are behind the number, subtract the number of dots from 13 to get the production month. Below is a detailed introduction to the coding of car glass: 1. Date reading method: The number represents the year, small dots represent the quarter (there are 4 quarters in a year, with a maximum of 4 small dots), and large dots represent the month within the quarter (a quarter has 3 months, with a maximum of 3 large dots). 2. 3C certification: The authenticity of the glass determines its shatter resistance and the degree of harm to people after breaking. A qualified car glass product must have a 3C certification, and this certification mark must be clear and extremely difficult to scrape off with a fingernail or blade.