The double bottom rule requires two distinct lows at roughly the same price level, separated by an intermediate peak, with the bullish reversal only confirmed when price breaks and closes above the neckline. A double bottom is characterized by two well-defined lows at roughly the same price level, with the standard rule of thumb that lows should be within 3-4% of one another.
There must be an existing trend to reverse, and a significant downtrend of several months should be in place.
The second trough should form a low within 3% of the previous low, volume on the ensuing advance should increase, and the formation is not complete until the previous reaction high is taken out.