Hi, If you are enquiring of the British system, as I understand it, from 1477 to 1575 it was 18 carat, from 1575 to 1798 it was raised to 22 carat, in 1798 the 18 carat standard was reintroduced as well as the 22 carat. 1854 saw the introduction of 9, 12 and 15 carats, In 1932, 12 and 15 carats were...