Sorry to obsess over retracement levels so much, but this newfound discovery (for me) has been terribly helpful, And yes, as King of ProphetCharts, I've already initiated a suggestion for a feature related to this that will help us out.
Anyway, the 870 level has been quite helpful today. So far, we've managed to keep below it over the past hour or so. The thing that's of most interest is to see if we can make it below the low so far of 859. That might get some wave 5 action really going.