0,1,1,2,3,5,8,13,21,34,55  ....

The next number is found by adding up the two numbers before it.

Golden ratio  1.618.

Fibonacci ratio 23.6%,38.2%,(50%),61.8%,78.6%,100%

fibonacci extention 161.8%,261.8%

The stock have a running up,then it may retrace. The ratio may be used to predict the possible support levels. The extention may be used to pridict future price target.

A lot softwares have the drawing tool. It can be a reference point.