Very Long-Term View of the Cash SPX
This very long-term chart shows that in 2015 at a price of 2158.70, S&P 500 (SPX) traveled 1491.91 points off of the March 2009 low, which equaled the distance traveled between Oct 1974 and March 2000.
If we extrapolate from a 1:1 ratio, to the next Fibonacci relationship, or 1.236 x the distance of the 1974 to 2000 advance, then we arrive at a next target of 2510.79.