A: The Dow Jones Industrial Average is an index that tracks the performance of 30 publicly traded stopcks. It is considered a barometer of how the stock market is performing.

The Dow Jones Industrial Average is calculated by adding up the per-share price of each stock, then dividing it by a regularly adjusted number (recently 0.1974). This means stocks with the highest share price are weighted most heavily (American Express was recently the highest, at $154 per share), unlike the S&P 500, which weights companies based on their size.

The 30 companies included in the Dow, which are selected by the editors of the Wall Street Journal, haven't changed much since the index was created in 1896. On November 1, 1999 several changes were made -- Microsoft, Intel, Home Depot and SBC Communications -- replace four old standards. Sears had been on the Dow since 1924, Union Carbide since 1928 and Chevron and Goodyear since 1930

The last change took place in March 1997, when Hewlett-Packard, Johnson & Johnson, Wal-Mart and what is now Citigroup replaced Texaco, Bethlehem Steel, Woolworth and Westinghouse Electric.