Where was the original serial number hm produced?

Does the subject want to ask "where is the beginning of Apple serial number hm produced?" Vietnam. The serial number of the Apple device is 12 digits, which consists of letters and numbers. The serial number contains information such as origin, production date, production cycle and equipment identification number. The first letter of the iphone serial number represents the origin code of the iPhone, H is produced in Vietnam, F is produced by Foxconn in Zhengzhou, and C is produced by Foxconn in Shenzhen. The second and third digits of the serial number represent the production line of origin; The fourth digit of the serial number represents the generation year, which is represented by 20 letters and rounded off once every six months.