Twitter has closed a deal to purchase Bluefin, a TV analytics firm, in what Business Insider says is the company's largest acquisition to date. There's been no firm figure attached to the sale yet, but if BI is correct it would mean Twitter spent more than the $40 million it shelled out for TweetDeck two years ago. As for why the company would invest so much in a social analytics business, Twitter is keenly aware of the close relationship between TV and your timeline. The microblogging platform has quickly risen to become the dominant second screen as millions of viewers tune into (and tweet about) major events like last night's Super Bowl.

These spikes of activity have done wonders for Twitter's brand, but the company has so far lacked a clear method of monetizing that success. Bluefin could help Twitter establish clear metrics to share with advertisers that prove just how engaged its user base is.

Convincing ad buyers to spend big requires clear, understandable metrics

In December Twitter revealed another way it plans to do that: a partnership with Nielsen will produce a new Nielsen Twitter TV rating that measures reach across the social service. That's set to debut before the fall 2013 TV season, though Bluefin could feasibly allow Twitter to pursue its own solution in the future. Ultimately it's about convincing huge brands to spend big on Twitter ads, and clearly the company is working hard to make that decision more appealing.