An employment contract or contract of employment is a kind of contract used in labour law to attribute rights and responsibilities between parties to a bargain. The contract is between an "employee" and an "employer". It has arisen out of the old master-servant law, used before the 20th century. Employment contracts relies on the concept of authority, in which the employee agrees to accept the authority of the employer and in exchange, the employer agrees to pay the employee a stated wage (Simon, 1951). Terminology A contract of employment is usually defined to mean the same as a "contract of service". A contract of service has historically been distinguished from a contract for the supply of services, the expression altered to imply the dividing line between a person who is "employed" and someone who is "self-employed". The purpose of the dividing line is to attribute rights to some kinds of people who work for others. This could be the right to a minimum wage, holiday pay, sick leave, fair dismissal, a written statement of the contract, the right to organise in a union, and so on. The assumption is that genuinely self-employed people should be able to look after their own affairs, and therefore work they do for others should not carry with it an obligation to look after these rights. Following the unification of the city-states in Assyria and Sumer by Sargon of Akkad into a single empire ruled from his home city circa 2334 BC, common Mesopotamian standards for length, area, volume, weight, and time used by artisan guilds in each city was promulgated by Naram-Sin of Akkad (c. 2254–2218 BC), Sargon's grandson, including those of shekels. Codex Hammurabi Law 234 (c. 1755–1750 BC) stipulated a 2-shekel prevailing wage for each 60-gur (300-bushel) vessel constructed in an employment contract between a shipbuilder and a ship-owner. Law 275 stipulated a ferry rate of 3-gerah per day on a charterparty between a ship charterer and a ship-owner. Law 276 stipulated a 2-gerah per day freight rate on a charterparty, while Law 277 stipulated a -shekel per day freight rate for a 60-gur vessel. In Roman law the equivalent dichotomy was that between locatio conductio operarum (employment contract) and locatio conductio operis (contract for services). The terminology is complicated by the use of many other sorts of contracts involving one person doing work for another. Instead of being considered an "employee",