2 standarrd deviations from the mean of last 20 days closing price...that is what the bands are. when the bands narrow it would obviously indicate that the trading range is narrow and indicates support. when a stock trades through the bands, the upper is bullish...an uptrend is in motion or technical breakout... if trades below the lower, its the opposite. Lately you can see ALU trades towards lower band but todays uptick was a slight reversal in price that could continue. Note the upper band and 200 day ave are soon to converge,... Alu is working through the massive sell-off from the 6+ level which required time. when the 50 trades above the 200 mov ave... that is a strong technical indicator - breakout...patience.