What a double bottom is, and what it is not

A double bottom is a shape on a price chart: a fall to a low, a rebound, a second fall that stops near the same level, and a second rebound. Drawn out, it looks like a W. The high between the two lows is conventionally called the neckline.

What traders say it means

The usual reading is that the first low attracted enough buying to stop the fall, the second low tested whether that buying was still there, and a move above the neckline shows it was. On that reading the pattern is a sign that selling pressure has exhausted itself. Plenty of traders act on it, and a number of them have written books saying so.

What the evidence actually supports

Less than the books suggest, and more than nothing. The best-known academic test of chart patterns, by Lo, Mamaysky and Wang in the Journal of Finance in 2000, ran automated pattern detection across US stocks from 1962 to 1996 and found that several patterns, including the double bottom, carried some incremental information beyond what was already in the price. "Some incremental information" is a long way from a reliable signal, and the study did not test whether trading on it would have made money after costs.

What it looks like in your own history

Expanding a closed position on the Performance page draws the daily candles for the period you held it, with your entry and exit marked on the sessions they happened in. That is the honest way to study a pattern: on trades you actually took, where the outcome is already known and nothing can be read into it after the fact.