the S&P 500 Index, CBOE S&P 500® 3-Month Volatility Index (VIX3MSM), CBOE S&P 500® 6-Month Volatility Index (VIX6MSM) CBOE S&P 500 1-Year Volatility Index (VIX1YSM). CBOE also calculates the Nasdaq-100® Volatility Index (VXNSM), CBOE DJIA® Volatility Index (VXDSM) and the CBOE Russell 2000® Volatility Index (RVXSM). There is even a VIX on VIX (VVIX) which is a volatility of volatility measure in that it represents the expected volatility of the 30-day forward price of the CBOE Volatility Index (the VIX®). Specifications The concept of computing implied volatility or an implied volatility index dates back to the publication of the Black and Scholes' 1973 paper, "The Pricing of Options and Corporate Liabilities," published in the Journal of Political Economy, which introduced the seminal Black–Scholes model for valuing options. Just as a bond's implied yield to maturity can be computed by equating a bond's market price to its valuation formula, an option-implied volatility of a financial or physical asset can be computed by equating the asset option's market price to its valuation formula. In the case of VIX, the option prices used are the S&P 500 index option prices. The VIX takes as inputs the market prices of the call and put options on the S&P 500 index for near-term options with more than 23 days until expiration, next-term options with less than 37 days until expiration, and risk-free U.S. treasury bill interest rates. Options are ignored if their bid prices are zero or where their strike prices are outside the level where two consecutive bid prices are zero. The goal is to estimate the implied volatility of S&P 500 index options at an average expiration of 30 days. The VIX is the volatility of a variance swap and not that of a volatility swap, volatility being the square root of variance, or standard deviation. A variance swap can be perfectly statically replicated through vanilla puts and calls, whereas a volatility swap requires dynamic hedging. The VIX is the square root of the risk-neutral expectation of the S&P 500 variance over the next 30 calendar days and is quoted as an annualized standard deviation. The VIX is calculated and disseminated in real-time by the Chicago Board Options Exchange. On March 26, 2004, trading in futures on the VIX began on CBOE Futures Exchange (CFE). On February 24, 2006, it became possible to trade options on the VIX. Several exchange-traded funds hold mixtures