The Dow Jones Industrial Average, Dow Jones, or simply the Dow, is a price-weighted measurement stock market index of 30 prominent companies listed on stock exchanges in the United States. Although the DJIA is one of the oldest and the most commonly followed equity indices, many professionals consider the Dow to be an inadequate representation of the overall U.S. stock market compared to broader market indices such as the S&P 500 or Russell 3000 Index. The DJIA includes only 30 large companies and is a price-weighted index, unlike later stock indices which use market capitalization. Furthermore, the DJIA does not use a weighted arithmetic mean. The value of the index is the sum of the stock prices of the companies included in the index, divided by a factor which is currently approximately 0.152. The factor is changed whenever a constituent company undergoes a stock split so that the value of the index is unaffected by the stock split. First calculated on May 26, 1896, the index is the second-oldest among the U.S. market indices. Wikipedia