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 manufacturing equipment specialist MKS Instruments (Nasdaq: MKSI) fell as much as 10% in early trading on average volume. The stock has since recovered, down less than 1% as of this writing.

So what: What gives? MKS ruined a perfectly good third-quarter report with a dour Q4 outlook. Let's cover the good news first. Q3 revenue fell 12% to $194.5 million while adjusted earnings dropped 19% to $0.58 a share. Analysts were more pessimistic, expecting just $0.48 a share on $190.6 million in revenue.

Now what: The bad news? Wall Street expected MKS to make up the shortfall and then some in Q4. Instead, management forecast $0.18 to $0.31 in adjusted earnings on $145 to $165 million in revenue -- well off not only last year's totals, but also the $0.43 and $182.7 million analysts were expecting. The intraday rally suggests Big Money investors may be trying to catch this falling knife. Be careful following them, Fool: You might get cut. Do you agree? Would you buy shares of MKS Instruments at current prices? Please weigh in using the comments box below.

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Fool contributor Tim Beyers is a member of the Motley Fool Rule Breakers stock-picking team. He didn't own shares in any of the companies mentioned at the time of publication. Check out Tim's portfolio holdings and Foolish writings, or connect with him on Google+ or Twitter, where he goes by @milehighfool. You can also get his insights delivered directly to your RSS reader.

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