Yesterday I updated my chart of the S&P 500 and the 50-day moving average. We saw our favorite index surge 2.25% to rise back above this benchmark indicator.

Today the S&P 500 had a 2.81% selloff, taking it back below the 50-day MA — a disappointing way to end the week. And unfortunately the volume was 15.4% higher than yesterday's advance. We'll post the occasional Stockcharts.com snapshot as this "encounter" plays out.