How Do You Read the S&P Index Historical Chart?

How Do You Read the S&P Index Historical Chart?

Historical charts on Yahoo! Finance for the Standard and Poor's 500 index, known as the S&P 500, show the price of the index graphed over time. The S&P 500 is an index of the most widely held 500 U.S. companies on the Nasdaq and New York Stock Exchange, according to Kimberly Amadeo for About.com.

The S&P 500 began trading on March 4, 1957, says S&P Dow Jones Indices LLC. For the 10-year period ending July 31, 2015, the index had a low price of $735.09 in February 2009 and a high of $2,107.39 in May 2015, states Yahoo! Finance. The index has never fallen below $500 since first reaching that price in 1995. The price of the S&P has increased 20 times from 1980 to 2015.

The S&P 500, by definition, shifts the companies included based on how widely they are held and restricts certain companies from inclusion. The minimum share price for an S&P 500 company is $1, and the minimum market capitalization for an S&P 500 company is $5.3 billion, notes Amadeo. In 1980, IBM was the largest company in the S&P but was removed from the index in 2000. The market capitalization of the top 10 companies combined in 1980 is about half of the market capitalization of 2015's largest S&P company, Apple, explains ETF Database.com.