At approximately 12:55 ET today, the Dow Jones Industrial Average fell to 7188.77, crossing below its October 2002 low value of 7197.49, reaching the lowest values seen since October 1997.
In October 2007, the DJIA set a high value of 14198.10, so we have seen a 7009.33 point drop from the high, which is a 49.4% decline. (UPDATE: We made it down to 49.9% by the close today!)
In short, we are on the verge of completing a 50% decline on the Dow in 16 months.
From the DJIA high of 386.10 in September 1929, it took 13 months to complete a 50% decline to 193.05 in October 1930, and when in July 1932 the worst was finally over 34 months after the high, the Dow had declined 89.5% to an all-time low value of 40.56.
How low will the Dow go? Who knows? There is no strong long-term trend line of technical support above 1000 keeping the Dow from collapsing further. Such a collapse would represent a 93% decline from the 2007 high -- a little more than during the 1930's, but in the same neighborhood.
The chart here shows changes in the Dow Jones Industrial Average since October 1928 in terms of percentages rather than points to make comparisons across the decades easier. (That's what base-10 logarithmic scales are all about.)
Here are a few key milestone values to consider on the way down that might be used as an excuse to stop the collapse:
7331 05/1997 close (UPDATE: Oops -- we blew through that level today, too, when we closed at 7,115!)
7009 -- 04/1997 close
6971 -- 10/1997 low
6583 -- 03/1997 close
5424 -- 61.8% decline (a key technical level)
3739 -- 11/1994 close
3639 -- 11/1994 low
3625 -- 06/1994 close
3552 -- 04/1994 low
3636 -- 03/1994 close
2442 -- 10/1990 close
2354 -- 10/1990 low
1834 -- 11/1987 close
1616 -- 10/1987 low
1132 -- 06/1984 close
1105 -- 05/1984 close
1082 -- 06/1984 low
0901 -- 08/1982 close
0809 -- 07/1982 close
0770 -- 08/1982 low
Look at the chart in the link above and you will see an interesting change in the slope of the trend line in mid 1994.
My best guess for a bottom in the current market is the 1994 low of about 3552 since that point in time also represents a milestone in politics. It was when Conservatism changed from being a philosophy to being a religion, and that brought with it consequences that filtered into the marketplace.
I hope I'm wrong. If 3552 doesn't hold, then there really is nothing technical stopping us from going all the way to 1000.