This British Standard specifies the general design requirements and test procedures for two grades of pressure cabin altimeters for aircraft:
Grade Ⅰ: for use with the pressurization control system, having a range of —2000 ft to +20 000 ft.
Grade Ⅱ: for use by the pilot, having a range of —2 000 ft to +30 000 ft.
BS G 190:1964 history
1964BS G 190:1964 Specification for cabin altimeters for aircraft