//@version=6
indicator("Workshop 04 Relative Strength", overlay=false)
other = input.symbol("AMEX:SPY", "Comparison")
length = input.int(20, "Return bars", minval=1)
[peer, peerTime] = request.security(other,
    timeframe.period, [close, time_close],
    gaps=barmerge.gaps_on, lookahead=barmerge.lookahead_off)
aligned = not na(peer) and peerTime == time_close
baseOK = aligned and aligned[length]
ownReturn = (close[length] > 0 ?
    100 * (close / close[length] - 1) : na)
peerReturn = (peer[length] > 0 ?
    100 * (peer / peer[length] - 1) : na)
plot(baseOK ? ownReturn : na, "Chart return",
    color=color.blue, style=plot.style_linebr)
plot(baseOK ? peerReturn : na, "Peer return",
    color=color.orange, style=plot.style_linebr)
plot(baseOK ? ownReturn - peerReturn : na,
    "Return difference", color=color.gray)
hline(0, "Zero", color=color.gray)