Econintersect: There is an excellent web site (Priced in Gold) which presents valuation data of various entities priced in ounces (or grams) of gold compared to the usual metric of observation, the U.S. dollar. The article they have posted on stock market valuations over a timeline longer than 130 years is very informative. There have been three huge stock market bubbles, each one almost exactly double the previous one.
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