Well this has certainly been an impressive move. I wrote a post yesterday looking at the stats for daily and weekly 3SD (three standard deviations from 20 period MA) punches, and the last time that a weekly punch through the 3SD lower band like the one we saw on Friday was at the collapse of France before the German attack in May 1940. If we close down hard today then this decline will, in this respect, have done what the declines in 2000 (Tech crash), 1998 (Russian crisis and LCTM failure), 1997 (Asian crisis), 1994 (bonds crash), 1987 (no clarification required I hope), and others all failed to manage. You can see that post here.
That said, we are a long way from today’s close and on the four equivalent punch closes through the 3SD daily lower band, three of those went lower the next day, with AM declines of 1.8% (equiv to 1934), 2.5% (equiv to 1920) and 3.7% (equiv to 1897). All four closed up with rises ranging between 3.2% and 5%.