Although we don't believe in timing the market or panicking over market movements, we do like to keep an eye on big changes -- just in case they're material to our investing thesis.

What: Shares of USG Corp. (NYSE: USG) are down 10% today on unusually high volume.

So what: With over an hour left in the trading day, nearly two times the average number of shares had traded hands. This high-beta stock looks to be suffering from an overall market decline and high oil prices, which may lead to lower demand in the future.

Now what: I wouldn't read into this move too much considering the overall market decline today. USG has a beta of 2.77, meaning it should (hypothetically) move 2.77 times what the market moves, and with the S&P down 2% as I am writing, the move is only slightly higher than expected. The company hasn't released any news; I don't see a reason to change the investment thesis on USG today.

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