The index plot will turn a purplish color when you are plotting on top of it. To change the time periods replace each instance of 21 in the formula with the desired number of periods and also change the time periods in the Beta custom indicator. Drag the price plot of the index your comparing, into the chart of the security. Drag this custom indicator from the Quick List and drop it onto the price plot of the index. Note, this formula is set to calculate beta over 21 periods.
Beta is a measure of volatility of one security against another.
A value greater than one indicates the stock is more volatile than the index. Load the security you want to check the alpha on. Then plot the custom formula for Alpha. Load the security you want to check the alpha on. Then plot the custom formula for Beta.