study(title="TSP Retracement 90", shorttitle="TSP Retracement 90", overlay=true)
basePeriods = input(90, minval=1, title="Retracement 90")
donchian(len) => avg(lowest(len), highest(len))
baseLine = donchian(basePeriods)
plot(baseLine, color=#991515, title="Base Line")