# BOLLINGER BAND

NSE:JETAIRWAYS   JET AIRWAYS INDIA
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BOllinger band is plotting standard deviation 2 from mean over a period of days . why it is not symmetric ?

Hello ,
Answer was very very simple , Its not un-symmetric , Its perfectly symmetric
Look at Bollinger band values 493 , 508 , 524 - 15 points apart ,
visually it doesn't look symmetric because the middle band is at angle ,
we can't judge visually once the reference point becomes tilted.

I think this is resolved now , It was at back of my mind for so many days.
My first answer would be we cant take points for comparison by drawing vertical lines that will only work when middle band is flat (i.e completely horizontal) , If the middle band has a slope than you to draw a line perpendicular to slope and than compare the upper/lower points on this perpendicular , you will find them equal.

I will confirm abt this.
neneram
@neneram, yes . But let us think a little bit on the formula how the bollinger band is calculated . It takes the clossing prices of the stocks. Calculates the mean and standard deviation.
Bollinger upper band = mean + 2 * standard deviation
Bollinger lowerband = mean - 2 * standard deviation

So the distance from mean on lower side and upper side is always equal. so from the moving average line, the distance of upper and bollinger band must always be same. If this is true, then how bollinger expansion take and contraction takes place ? I am searching for the answer and high huge set of questions like this. But everyone wants money to clarify my doubts.