The S&P 500 is widely considered to be the best indicator of how the U.S. stock market is doing, and it's easy to understand why. After all, it contains 500 of the largest companies in the United ...

Image source: Getty Images. For example, the largest companies in the United States, Apple (NASDAQ: AAPL) and Microsoft (NASDAQ: MSFT), make up 6.8% and 6.2% of the entire weighting of the S&P 500 ...