Coinage and currencies

A currency is a unit of money (or monetary unit). Typically, each country has given monopoly to a single currency, controlled by a state owned central bank, although exceptions from this rule exist. Several countries can use the same name, each for their own currency (e.g. Canadian dollars and US dollars), several countries can use the same currency (e.g. the Euro), or a country can declare the currency of another country to be legal tender. Each currency typically has one fraction currency, valued at 1/100 of the main currency: 100 cents = 1 dollar, 100 centimes = 1 franc. However, some currencies use a fraction of 1/10 (and a very few some other value such as 1/5 or 1/20), or do not have a minor unit currency at all.

The history of currencies follows the history of money closely. Although any form of representational money can be considered currency, the term is typically applied to standardized coinage, and the systems that developed from it. Prior to the introduction of standard coinage, calculating the value of a metal-based money required several steps. First the metal was tested on a touchstone to calculate the quality, then it was weighed, and then the two values were multiplied. Thus if someone alloyed gold and lead (which was a common cheating process) the metal's weight was multiplied by the percentage of gold to get the weight of the gold alone.

Coinage was introduced to simplify this process. Coins were created of a set weight and gold quality, and then stamped to prove their worth. No measurement was needed, as long as the original values were known. Of course one could use an alloy with the same stamp as the coin to cheat, but the stamps were complex and thus difficult to duplicate (at the time). More modern currency systems developed from the introduction of coins. The process started with the replacement of the original metal, with a coin representing it. The gold itself was kept safe in government vaults. Examples of this system in the past was the gold standard, where the US Dollar was backed with gold stored at Fort Knox, and the British Pound Sterling, which was backed by one pound of sterling silver.

The evolution continued, first to paper representations of the same standard, and finally to removing the metal altogether - the paper itself is considered to be valuable. In order to prevent forged currency, various technologies such as watermarks are inserted into most paper currencies. In the early 21st century, the use of RFID tags has been proposed to track bank notes which were illegally obtained. Such efforts have been criticized by privacy advocates.