The troy ounce in modern use is essentially the same as the British Imperial troy ounce (1824–1971), adopted as an official weight standard for United States coinage by act of Congress on May 19, 1828.[11] The British Imperial troy ounce (known more commonly simply as the imperial troy ounce) was based on, and virtually identical to, the pre-1824 British troy ounce and the pre-1707 English troy ounce. (1824 was the year the British Imperial system of weights and measures was adopted; 1707 was the year of the Act of Union which created the Kingdom of Great Britain.) Troy ounces have been used in England since the early 15th century, and the English troy ounce was officially adopted for coinage in 1527. Before that time, various sorts of troy ounces were in use on the continent.(Wiki)