The rapid increase in the number of different values that can be represented as bits are added is exponential growth i.e. it doubles with each extra bit. After doubling 16 times we can represent 65,536 different values, and 20 bits can represent over a million different values. Exponential growth is sometimes illustrated with folding paper in half, and half again. After these two folds, it is 4 sheets thick, and one more fold is 8 sheets thick. 16 folds will be 65,536 sheets thick! In fact, around 6 or 7 folds is already impossibly thick, even with a large sheet of paper.