The ratio between any two successive numbers in the Fibonacci sequence, known as phi (f). The ratio of any number to the next higher number is approximately 0.618 (known as the Golden Mean or Golden Ratio), and to the lower number approximately 1.618 (the inverse of the Golden Mean), after the first four numbers of the series. The three important ratios the series provides are 0.618, 1.0 and 1.618.
