Thunderbolt RSI

//@version=2
study(title="Thunderbolt RSI", shorttitle="Thunderbolt RSI 80/20")
src = close, len = input(7, minval=1, title="Length")
up = rma(max(change(src), 0), len)
down = rma(-min(change(src), 0), len)
rsi = down == 0 ? 100 : up == 0 ? 0 : 100 - (100 / (1 + up / down))
plot(rsi, title="thunderbolt", color=yellow, linewidth=2, transp=1)
band3 = hline(0, "zero", black, 2, 0)
band4 = hline(100, "100", black, 2, 0)
band1 = hline(80, "OB", red, 2, 1)
band0 = hline(20, "OS", green, 2, 1)
fill(band1, band0, color=gray, transp=70)
fill(band4, band1, color=#4985E7, transp=70)
fill(band3, band0, color=#4985E7, transp=70)