This is a Japanese hiragana

し

The unit symbol refers to the letter representation of the physical quantity unit. If the length unit "meter" is expressed by letters as "m", it is a unit symbol. All unit symbols are arranged in straight letters.

This is clear and well known in the specification. But some of these unit symbols should be capitalized and some should be lowercase. For example, the length unit symbol m should be lowercase; The unit symbol n of force should be capitalized and kg should be lowercase; Pressure, pressure and stress units Pa P should be capitalized and a should be lowercase; M in MPa is capitalized and k in kN is lowercase. Energy, work, SI multiple unit eV, where e is lowercase, v is uppercase, and so on. The author writes these questions casually, while the editor often pays little attention to them when editing. Many magazines and books made similar mistakes.