Each season normally consists of 13 rallies driven on surfaces ranging from gravel and tarmac to snow and ice. Points from these events are calculated towards the drivers' and manufacturers' world championships. The driver's championship and manufacturer's championship are separate championships, but based on the same point system. This means, for example, that Petter Solberg driving for Subaru can win the driver's championship but Citroën can win the manufacturer's championship, which is what happened in 2003, and again in 2006 and 2007 when Sébastien Loeb took his third and fourth WRC titles but Ford won the manufacturer's championship.