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 miner Arch Coal (NYSE: ACI) jumped 10% after the company released disappointing earnings. Yes, you read that right.

So what: Third-quarter revenue rose 37% to $1.20 billion, but fell below estimates of $1.22 billion. Earnings per share was also disappointing at $0.08 per share, well below the $0.13 analysts were expecting.

Now what: How can your stock go up after a disappointing earnings announcement? For one thing, much of the bad news was already priced into the stock, and when management reaffirmed full-year guidance and announced some recent contracts, the market got excited. The company said that it expects exports to be strong as Asian steelmakers continue their demand, so the future might be brighter than the market thought a few weeks ago.

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