Fibonacci retracement & extension to measure price-action. The interaction between actionary and reactionary waves can be understood with the Fibonacci tools.
Market conditions can be similar in some aspects; however, they are always different comparing to the past. To rely on fibonacci tool for trading it is necessary to have a reason to use it. In other words, you use it not trying to replicate previous scenarios, but to measure what is going on in present.
Happy trading!