Is Another October Surprise in the Works? -- Seeking Alpha: "The mountain started shaking in the summer of 1929 and by autumn panic gripped the markets, resulting in a 2-day, 23% sell-off in the DJIA. By the middle of November 1929, the DJIA had lost 40% of its value.
What happened next is crucial to understanding what is happening right now. The market then made a valiant attempt to rally, bringing back many investors from the sidelines as the Dow mounted a furious charge into 1930. However, the rally didn’t stick, conditions worsened and by the time 1932 rolled around the venerable index had lost 89% of its value. It would take 25 years for the Dow to recover that lost value in nominal terms."