relative strength to BTC

Measure the relative strength of a crypto compared to Bitcoin.
Pair trading strategy:
Pairs trading is a strategy in which a trader matches long and short positions of two stocks that are perceived to have a strong correlation to each other and are currently trading outside of their historical relative strength range.

Formula:
a: tickerid, the crypto selected
b: BTCUSD Bitfinex

as: security a, (close-close[1])/close[1]*100+100)
bs: BTC, (close-close[1])/close[1]*100+100)
rs= (as-bs)/bs*1000

Green line is a moving average.