The strength bar is a high level overview of back testing that we have performed on a stock. The amount of color filling the bar is representative of how many of the last 10 algo alerts that ended up with a positive back test.
When the strength bar is low, you should exercise greater caution in your trade. This means that historically, the back tests have shown weaker profitability on the stock after an algo.
When the N/A symbol is shown, it means we do not have enough recent data to confidently calculate a strength score for that algo alert.