Commodity money as a theoretical backing for federally issued "gold certificates" to substitute for the gold. Between 1933 and 1970 (when the U.S. officially left the gold standard), one U.S. dollar was technically worth exactly 1/35 of a troy ounce (889 mg) of gold. However, actual trade in gold bullion as a precious metal within the United States was banned after 1933, with the explicit purpose of preventing the "hoarding" of private gold during an economic depression period in which maximal circulation of money was desired by influential economists. This was a fairly typical transition from commodity to representative to fiat money,
Commodity market and (platinum). However, most ETCs implement a futures trading strategy, which may produce quite different results from owning the commodity. Commodity ETFs trade provide exposure to an increasing range of commodities and commodity indices, including energy, metals, softs and agriculture. Many commodity funds, such as oil roll so-called front-month futures contracts from month to month. This provides exposure to the commodity, but subjects the investor to risks involved in different prices along the "term structure", such as a high cost to roll. ETCs in China and India gained in importance due to those countries' emergence as commodities consumers and producers.