Here are the data for Indianapolis 500 races:

Year	Winner	Car	Time (h)	Speed	Car #
1911	Ray Harroun	Marmon Model 32	6.7022	74.602	32
1912	Joe Dawson	National	6.3517	78.719	8
1913	Jules Goux	Peugeot	6.5848	75.933	16

Is year a categorial variable or a quantitave variable? Why? If year is a quantitave varible, please tell the quantity of what is measured and identify the unit in which it was measured (or note that the variable doesn't have unit).