Do you know...
that purity is a number expressing the weight content of a precious metal in an object (bar, coin, jewel, etc.) and is usually indicated in thousandths (for example, 750/1,000 indicates an alloy with 75% precious metal content and 999.9/1,000 an alloy with 99.99% precious metal content)? However, purity can also be expressed in other, older or regional units. The most important of these is the carat, which is still used in jewellery (not to be confused with the carat, e.g. the metric carat, as a unit of mass used for gemstones and pearls). An object of theoretically pure content is designated as having 24 carats. Gold of 750/1,000 purity is therefore 18-carat gold, for example. The carat is not a practical unit for gold bars and coins, as it is not sufficiently precise (although a non-whole number, or the gran, which is one-twelfth of a carat, can be used) and the alloy purities used in jewellery do not always match those used for coins.
(video with English subtitles)