Find a stock selection formula that the stock price hit the lower rail of the bollinger band on that day?

To touch the lower rail of the bollinger band, we must first explain the formula of the bollinger band, because there are two formulas of the bollinger band in the communication software, one is traditional and the other is unconventional.

The picture below shows the tradition above and the unconventional below.

The following formula is the lowest price of non-traditional bollinger bands touching the lower rail of bollinger bands.

XG:L & lt； MA (closing, 20)-2*STD (closing, 20);