The formerly little-watched Baltic Dry Goods Index had by November 10 2008 fallen more than 90% from its May peak.

Why this is important is that this index is a "leading indicator", something that anticipates economic shifts. The value of the index is that it is intimately wound up with the global "real economy", and is not subject to speculation.

In other words it is not a financial indicator such as a stock market index or a measure of sentiment such as a consumer confidence index.

The index measures the price of moving by sea bulk dry goods that are the raw material of manufacture, such as iron ore or grain. It does not measure the cost of moving goods, which tend to be manufactured items, in containers.

The UN Council on Trade and Development (Unctad) suggested recently that its Review of Maritime Transport, "... the decline in the index indicates that the financial crisis has spread to international trade, with negative implications for developing countries, especially those dependent on commodities."

For South Africa, a country whose economic fortunes are very much dependent on commodities, this is bad news indeed.

For an explanation of the index, and also a reminder of how optimistic one could be five years ago, go to Daniel Gross's 2003 article on the index on Slate.