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 mining equipment maker Joy Global (NYSE: JOY) sank as low as 9.6% on Thursday after its full-year guidance disappointed Wall Street.

So what: Joy Global's second-quarter results managed to top estimates, but management's cut to its 2012 outlook reignites serious concerns over its exposure to the shaky global economy. Management cited lower orders for the weak guidance, suggesting that the trouble in Europe and China's slowing growth expectations are weighing more heavily on demand than investors had expected.  

Now what: Management now sees 2012 EPS of $7.15-$7.45 on revenue of $5.5 billion-$5.7 billion, versus Wall Street's view of $7.60 and $5.7 billion. "Even though there is upside to the current market conditions, the continuing uncertainty will keep mining companies cautious," warned president and CEO Mike Sutherlin. Of course, with the stock hitting a new 52-week low and trading at a forward P/E of about 6.5, much of the gloomy outlook might already be baked into the price.

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