• phi, Φ
The relationship between a number in the Fibonacci sequence and the previous number more and more closely approaches the irrational number Φ, the longer the sequence is continued. And Φ describes nothing other than the golden section.
• psi, Ψ
An important part is also played by the golden angle which divides the angle of 360° in the proportions of the golden section. As an angle smaller than 180° proved to be more handy in practice the smaller of the resultant angles is called the golden angle