The Dow Jones Industrial Average had an intra-day low of 40.56 on this date in 1932, its Great Depression bottom. It closed that day at 41.22.
34 months earlier it had been at 381.17; the drop was 89.3%.
(For comparison, we’re 21 months into the current bear market, down 43.7% since October 2007.)
The Dow did not reach the September 1929 level again in inflation-adjusted value until 1954.