Complex sentence: Button used only one chassis over the course of the season (most drivers change chassis several times), having driven it in every practice and qualifying session and race, meaning that he won the World Championship in the oldest car on the grid.
Split into simpler sentences: Button used only one chassis over the course of the season (most drivers change chassis several times), having driven it in every practice and qualifying session and race. Meaning that he won the World Championship in the oldest car on the grid.