Bollingerband double

//@version=2
study(shorttitle="jchinh2BB", title="Bollinger Bands double", overlay=true)
source = close
length = input(20, minval=1), mult1 = input(2, minval=0.001, maxval=50), mult2 = input(1, minval=0.001, maxval=50)
basis = sma (source, length)
dev1 = mult1 * stdev(source, length)
dev2 = mult2 * stdev(source, length)
upper1 = basis + dev1
lower1 = basis - dev1
upper2 = basis + dev2
lower2 = basis - dev2
plot(basis, color=green)
plot(upper1, color=green)
plot(lower1, color=green)
plot(upper2, color=green)
plot(lower2, color=green)