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 Plexus (Nasdaq: PLXS) fell close to 11% in early trading and closed down 9% after reporting lower than expected third-quarter revenue and offering weak Q4 guidance.

So what: Plexus, a contract manufacturer of electronics, booked $559.2 million in Q3 revenue, missing the consensus estimate by more than $7 million. Think that's bad? Guidance was even worse. Plexus now expects to earn $0.50 to $0.55 a share on $530 million to $560 million in Q4 revenue. Analysts were calling for $0.60 and $585.1 million, respectively.

Now what: Plexus CEO Dean Foate said customers cut demand for the second half of the year, leaving little reason for investors to remain enthusiastic over the short term. Do you agree? Disagree? Weigh in using the comments box below.

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Fool contributorTim Beyers is a member of theMotley Fool Rule Breakers stock-picking team. He didn't own shares in any of the companies mentioned in this article at the time of publication. Check out Tim'sportfolio holdings andFoolish writings, or connect with him on Google+ or Twitter, where he goes by @milehighfool. You can also get his insightsdelivered directly to your RSS reader.

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