FX:SPX500   S&P 500 index of US listed shares
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The standard deviations of the highs and lows are done separately. The result is Bollinger Band composite that works better for setting extreme points where the price will most likely not breach. The method for timing the entries are oscillators such as stochastics or Rsi .
These boundaries can then be used to set credit spreads such as call and put vertical spreads.

study(shorttitle="HL BB", title="High Low Bollinger Bands", overlay=true)
length = input(20, minval=1)
src = input(low, title="Source")
src2 = input(high, title="Source2")
mult = input(3.0, minval=0.001, maxval=50)
mult2 = input(3.0, minval=0.001, maxval=50)
basis = sma (src, length)
basis2 = sma (src2, length)
dev = mult * stdev(src, length)
dev2= mult2 * stdev(src2,length)
upper = basis2 + dev2
lower = basis - dev
plot(basis, color=orange)
p1 = plot(upper, color=red)
p2 = plot(lower, color=blue)
fill(p1, p2)
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