Why isn't there a forex currency index?

Just like the stocks are combined into NASDAQ for example, then why can't you combine the forex pairs and assign them a mathematical value???

Take a look here:
http://www.fxstreet.com/rates-charts/currencies-glance/

Fxstreet lists 34 forex pairs.

Benefits:
- Less risk.More pairs - less risk. Traders will take advantage because the market is open day/night in contrast to the daily trades among the stock market. That said, the forex traders gain several times more action with reduced risk,

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