Below is a real-time plot of the S&P 500 (SPY) against a model of the implied value for the S&P 500 as derived from a collection of related assets (volatility (XIV), treasury bond prices (TBF), and high yield corporate credit (HYG)). With this model a trader can place arbitrage trades to take advantage of prices as they diverge and recouple during the day. For an overview on this tool please see this post. For specifics on using it to trade see this post.
(Real-time data begins ~9:35AM ET)