Tyler and Cameron Winklevoss have not only been hard at work on on an ETF for Bitcoin but they just announced that the Winklevoss Index is now being displayed via Bloomberg under WINKBTCO.
The Winklevoss Index (also known as Winkdex) is a pioneering effort in the analysis and presentation of global bitcoin pricing and currently uses data from the most active qualified U.S. dollar denominated bitcoin exchanges. Winkdex is operated by Math-Based Asset Index, LLC.
The index provides a blended price for bitcoins. Winkdex is calculated by blending the trading prices in U.S. dollars for the top three (by volume) qualified Bitcoin Exchanges during the previous two hour period using a volume-weighted exponential moving average. This proprietary formula weights transactions proportionally by volume as well as exponentially by time to give greater weight both to higher volume transactions and more recent transactions.
The twins have also announced they will soon be rolling out an API for the developer community to build upon. More information regarding the formula can be found here: http://winkdex.com/#/formula