The SPY:$VIX ratio chart is best used to identify market bottoms. Each time the Percentage Price Oscillator (PPO 1,10,0) reading moves below -10 the S&P 500 (SPY) has reached a short-term market bottom.
The VIX has an inverse relationship to the price of the S&P 500. Thus, we often see the VIX making new highs as the market is making new lows. When the 2-period RSI of the VIX is above 90 we'll be looking to go long.
