This measurement takes it name from the city of Troyes, France, where dealers in precious stones and metals gathered in medieval times. Gold and other rare metals are still measured in troy ounces (31.1035g). A standard international gold bar weights 400 troy ounces (12.44kg).
This measurement is used by typographers and printers and refers to the size of a letter such as an x. One point is equal to 0.3528mm, so the 6-point type in telephone directories is 2.116mm high.
Speed at sea is measured in knots, which is the time it takes a ship to travel the length of a knotted rope. A knot is now the same as a nautical mile, which is 1,852m.
The height of horses is measured in hands. The measurement is usually taken from hoof to the highest point on the animal’s shoulder. One hand is 10.16cm.
The weight of diamonds and other valuable gems is measured in carats. The word comes from the carob bean, which has a consistent weight of 0.2 of a gram.