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Teams only changed numbers when the Drivers' Champion was not driving for the previous No. Since the 1973 World Champion, Jackie Stewart, left F1 at the end of that season, the team leader for the constructors champion ( Ronnie Peterson) drove the No. But midway through that year, permanent numbers were trialled, and in 1974, permanent numbers were issued based on the Constructors' Championship positions in 1973. Up to 1973, the numbers were given out by the race organisers. Until 2013, the numbers were allocated with two rules: the previous season's World Champion used the number 1 following the Champion and his team-mate (car number 2), the teams were ordered by their position in the previous season's Constructors' Championship. This number cannot be reallocated unless the driver has not driven in the sport for two seasons. Only the World Champion is allowed to use number 1. Currently, drivers are allowed to pick their own number for their career from 0, 2 through 99. A Formula One car number is the number on a car used to identify a car and its driver.
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