The Winklevoss twins really do want to put their name into bitcoin - they have launched a blended bitcoin price index, the 'Winkdex' that they say reflects the true price of the digital currency. The index will be used to price the assets in the brothers' forthcoming bitcoin trust.

The Winkdex will be offered by Math-based Asset Index LLC, a company operated by the Winklevosses. It was announced today in the brothers' latest filing with the SEC, an amended version of its July filing describing the Winklevoss Bitcoin Trust.

The Winkdex uses the trading price in US dollars for the top three qualified bitcoin exchanges by volume across a two-hour period. It uses a volume-weighted moving average to set its price. It also weights the most recent transactions in the two-hour period greater than earlier transactions in the same window.

In time, the pair hope that the index will be used as a more general benchmark for the price of bitcoin, rather than purely as a way to determine the net asset value of the fund.

Price indices for bitcoin are becoming increasingly important given the volatile nature of the asset, and the delta that exists between various exchanges, which are themselves relatively young, and part of a still emerging market. The Winkdex's page, which shows six different exchange prices in addition to its own, is indicative of the large spread between different exchanges.

Average prices on LocalBTC (localbitcoins.com) were listed at around $760 on the site, for example, while pricing at troubled Mt Gox stood at just $262, at the time of writing. The Winkdex pegged bitcoin at $628.

The Winkdex joins CoinDesk's own Bitcoin Price Index, launched last September, which has a clearly defined set of rules outlining which exchanges it supports.

Like CoinDesk, MBAI has disqualified Mt. Gox from inclusion in its index. It attributed this to the recent freeze in bitcoin withdrawals, in addition to its backlog of US dollar withdrawals.

Along with today's amended SEC filing, the launch of the Winkdex is a signal that the Winklevoss brothers are moving closer to the launch of their ETF. The filing was expected, following an announcement by their lawyer last month. She predicted that the fund might be approved by the end of this year.

The latest version of the SEC filing referred to the Federal Senate hearings last year, in addition to the NYDFS hearings that took place in January. It highlighted the regulatory uncertainty that still exists around bitcoin. The Winklevoss twins will be particularly sensitive about this; they attended the hearings just days after the arrest of Charlie Shrem, the founder of now-defunct BitInstant which was one of their key investments. They distanced themselves from Shrem in a statement at the time.

The Winklevoss brothers claimed to hold 1% of all bitcoins when the initial ETF document was submitted last July.

Winklevoss photo via Shutterstock