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 capacitor manufacturer KEMET (NYSE: KEM) started out the day looking pretty good, but a 3% early rise turned into a 10.7% drop as the day moved on, all amid very heavy trading.

So what: KEMET's third-quarter report beat analyst expectations about the head and neck, but the earnings call unveiled a dismal outlook for the coming quarter, and all the good news was quickly forgotten. Specifically, the all-important book-to-bill ratio stands far below the magic 1.0 mark, and management sees its gross margins taking a serious hit from increasing materials prices. Close rivals Vishay Intertechnology (NYSE: VSH) and AVX (NYSE: AVX) hardly moved on KEMET's negative materials news, though.

Now what: The stock was delisted from the New York Stock Exchange in early 2009 and teetered on the edge of extinction, then made a scary-quick recovery when the stock was relisted again in November 2010. The balance sheet is still shaky but in much better shape than in the bad old days. Investor nerves are perfectly understandable with a background like that.

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Fool contributor Anders Bylund holds no position in any of the companies discussed here. We Fools may not all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors. The Motley Fool is investors writing for investors.