Here is a daily chart plotting FAS and FAZ. I’ve highlighted the price points at which they’ve met recently. I’ve drawn a regression-like line depicting their mutual decline.
The bottom study is a correlation study with a 30-bar lookback. As you can tell, I need to upgrade my image publishing skills. If you can’t read the values of the correlation, they start at -0.75 on the top and go down to -0.95 on the bottom. The current correlation value is -0.81. Not perfectly negatively correlated, but pretty close.
The prices at which they’ve met in chronological order is about $9.52, $9.17, $8.35 and $8.22. They started these shenanigans around April 13, 2009.