As the CD spins over the laser, the laser reads the digital code on the CD's surface (digital code is made up of 1's and 0's) . The numbers are "encoded" by tiny indentations, called pits, that determine whether the laser reads a number 1 (on) or a number 0 (off). The example to the left shows the laser beam reading one pit. If the laser passes over the pit, it reflects back to the CD player and reads the digital number 1. If not, then it reads a 0. There are millions of these pits, which make up the enormous digital code on every CD.