The inbuilt Bollinger band chart shows the top and bottom curves but the mid line is missing.
As per Mr. Bollinger 9Inventor): Bollinger Bands consist of:
an N-period moving average (MA)
an upper band at K times an N-period standard deviation above the moving average (MA + Kσ)
a lower band at K times an N-period standard deviation below the moving average (MA − Kσ)
So like to know how to make mid line in the chart.
Same is with Keltner band also.