I'm looking at a chart of October '87, and the Dow was about 2700 in the beginning of the month. Before we even got to that Wednesday (the 13th), the Dow was down to 2500. The volume really started ticking up on that 13th, 14th, 15th. The 19th and 20th were both the biggest-volume days of the selloff.

That's right. Actually, the interesting thing about 1987 is that most people incorrectly say 'it just came out of nowhere.' That the market was going up one day and suddenly crashed. And yet, we had a whole series of classic warning signs that the market was weakening. For example, the advance/decline line, which is a simple measurement of the number of stocks going up vs. the number of stocks going down, topped out in early April of 1987, showing that that was the point in which the largest bulk of stocks was starting to peak in price.

Our buying power index, which again is the measurement of the amount of buying enthusiasm present in the market, topped out in late March of 1987. From that point on, the market was still going higher but was doing so with less gas in the tank, so to speak. And also we run an index called the selling pressure index that measures the amount of selling activity present in the market in any given time, and that was in a strong uptrend pattern, particularly starting in early August. And during that last rally attempt -- the failed rally attempt in early September -- the buying power index was dropping at a very rapid pace and the selling pressure index was rising at a very rapid pace, showing that buying enthusiasm had really been lost and that the sellers were trying to dump stocks as quickly as they could. That all occurred almost two months ahead of the actual break in prices.

Not Your Father's NYSE

A question that has come up about your work is how are your buying power and selling pressure calculated. Is it proprietary, or is it something that anybody could find in the daily market data?

Well, it is proprietary in the sense that Coca-Cola is proprietary (laughs). In other words, you can look at a bottle of Coke and it will tell you exactly what the ingredients are, but they won't tell you how they cook it.

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