If we use the "mass on a spring" model, there is a clear formula for the frequency at which the mass goes up and down. The time between up (or down) cycles is proportional to the mass on the spring (The bigger the mass, the slower it moves).
If we think of the "mass" of the market, a good measure would be Market Capitalization. I had a hard time finding this value for 1929, so I decided to use GDP instead. To convert to 2008 dollars, I divided by CPI (consumer price index) to factor out inflation.
|CPI||Sqrt(m)||Ratio to 1929|
What this means is that 3.4 days today is equal to 1 day in 1929 (in terms of market momentum). So here's a plot of the stock market with 1929 scaled by value (using recent market highs) and by time (using here 2.8 days). The similarity is scary.