ProShares UltraShort S&P500 seeks daily investment results that correspond to twice the inverse of the daily performance of the S&P 500 Index. The S&P 500 Index is a measure of large-cap United States stock market performance. It is a float-adjusted market capitalization weighted index of 500 United States operating companies and real estate investment trusts (REITs) selected by an S&P United States Index committee through a non-mechanical process that factors criteria, such as liquidity, price, market capitalization and financial viability. Reconstitution occurs both on a quarterly and on an ongoing basis. It takes positions in securities and/or financial instruments that, in combination, should have similar daily return characteristics as –200% of the daily return of the index.