The letters of unit symbols are generally lowercase. If the company name comes from a person's name, the first letter of the symbol is capitalized. The letters of the prefix symbol indicate factors less than 106, all in lowercase; And the capital is greater than or equal to 106. The symbolic name of l is not derived from a person's name, but it is easily confused with Arabic numeral 1 when lowercase 1 is used. Therefore, 16 (1979) is the resolution of the international metrology conference: "As an exception, it is allowed to use 1 and L as units to increase the current sign." In current people's habits, when l is used alone, it is often capitalized. Such as 5l; When l and prefix are used together, use lowercase, such as 50ml, 50dl, etc. It is the legal unit of measurement in People's Republic of China (PRC), and ml is more suitable.