very simple and very useful:

you have a sharp rise or fall, the price makes a wedge or flag, you know there would be a correction, and then:

1. wedge will reverse the trend
   OR
2. flag will continue the trend

where is the limit for correction to take profit from a trading range or enter a new trend?

50% of the rally/drop

for example, look at below ETHUSDT chart:

the pink mark is slightly below 50% of the last drop. I may long till there or set up a short position from that level.