It's used to measure the performance of these corporations whilst also reflecting the state of the American economy and, to a degree, the world economy.
In spread betting and CFD trading, rather than being called the Dow, Dow Jones or Dow 30 it is often called 'Wall Street' or the 'US 30'.
The Plus500 chart above is usually based on the Dow Jones futures contract (not the daily market).
The Dow represents a selection of thirty of the biggest American public companies.
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The Dow Jones Industrial Average is the most well-known share index in the USA.
The shares included in it are weighted according to price; the index level represents the average of the shares included in it. The inclusion of a company in the Dow Jones Industrial Average does not depend on defined criteria.
Instead, an independent Wall Street Journal commission decides whether a share is to be included or excluded.
The Dow Jones was developed by Charles Henry Dow and originally contained just 12 American companies.