There have been many disputes over what makes production and modified cars when used in motorsports. Even under Fédération Internationale de l'Automobile (FIA), the exact definition of what was (or was not) a production car was unclear. This led to rules written in 1955. The term is defined for particular types of vehicles. It also means that a certain number of a model must be produced in order to qualify as "production". But it is another matter to enforce the rules. For example, the 1968 FIA rules state that "production" for sports cars need to have at least 25 identical cars produced within a 12-month period. They also were meant for normal sale to individual purchasers. However, FIA rules tend to allow a degree of modification from the original.