The Jones Index, also known as the Dow Jones Industrial Average (DOW), is a stock market index that tracks the performance of 30 large companies listed on the New York Stock Exchange. It is one of the oldest and most widely followed indices in the world and is often used as a benchmark for the overall performance of the US stock market. The index is calculated by taking the sum of the prices of the 30 stocks and dividing it by a divisor. The divisor is adjusted to account for stock splits and other corporate actions. The index is updated every 15 seconds during trading hours and is widely used by investors to gauge the performance of the stock market.