Perhaps the most familiar example of subscripts is in chemical formulas. For example, the formula for glucose is C6H12O6, meaning that it is a molecule with 6 carbon atoms, 12 hydrogen atoms and six oxygen atoms. Subscripts are also used frequently in mathematics to define different versions of the same variable; for example, in an equation x0 and xf may indicate the initial and final value of x, while vrocket and vobserver would stand for the velocities of a rocket and an observer.