Fineness is another way of measuring gold purity, popular in the West, expressed in parts per thousand. In this system, pure 24k gold is expressed as 1000 parts out of 1000. For example, to calculate 24k gold fineness, you need to divide 24k by 24k and multiply by 1000, which will give you a fineness of 1000. However, in practice, pure gold fineness is marked as 999.9 because there is likely to be a slight impurity in any gold. If you divide that number by 10, you will get the percentage value of 99.9%, which indicates the pure gold content in a piece.
Following the same logic, 14k gold fineness should have been marked as 583 (14/24 x 1000 = 583.333), but most manufacturers have adopted the European practice of making 14k gold slightly over 583, so 14k gold fineness is marked as 585.
It is worth mentioning that accepted tolerances on gold purity vary from country to country. For example, in the United States, the permitted negative tolerance is 0.3%, while in China, 1% is legally allowed.