Sch 6 para 1
Units of mass The units of mass used shall be the legal units within the meaning of the Weights and Measures Act 1985 relating to units of measurement . Subject to compliance with this condition, the following units are permitted— (a) SI units: kilogram, microgram, milligram, gram, tonne; (b) imperial unit: troy ounce, if weighing precious metals; (c) other non-SI unit: metric carat, if weighing precious stones. For instruments that make use of the imperial unit of mass referred to above, the relevant essential requirements specified below shall be converted to that unit, using simple interpolation.