Digital as in not granular. 1 and 2 are digital numbers. Vinyl records were analogue, CDs were digital. They also use binary gradients, i.e. ISO, 100,200, 400 800 and 1600 are based on the binary system: 1,2,4,8,16. i.e. a 4 bit binary number can represent 16 variables, 0 - 15.