This standard BS 2G 182:1975 Specification for pressure-driven machmeters for aircraft is classified in these ICS categories:
49.090 On-board equipment and instruments
This British Standard specifies the general design requirements and test procedures for machmeters of the following types.
1.1 Type A. Machmeter indicating a Mach scale range of at least 0.5 M up to a maximum scale reading of 1.0 M and of altitude range up to 50 000 ft, with maximum accuracy from20 000 ft to 40 000 ft, unless otherwise required by the individual specification.
1.2 Type B. Machmeter indicating a range extending above 1.0 M and of altitude range up to 60 000 ft with maximum accuracy in the region between the altitude limits 20 000 ft and 40 000 ft and in the indicated range of 0.7 M to 0.9 M.