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: Hewlett-Packard (NYSE: HPQ) dropped 12% in intraday trading today after the company issued disappointing guidance for the current quarter.

So what: HP delivered a nice upside surprise in its most recent quarterly earnings, with non-GAAP EPS of $1.36, compared to guidance of $1.28 to $1.30 and the consensus estimate of $1.29. But current-quarter guidance was for non-GAAP EPS of $1.19 to $1.21, versus a consensus estimate of $1.26, and revenue of $31.4 billion to $31.6 billion, versus a consensus forecast of $32.6 billion. 

Now what: Management also effectively guided down the second half of the fiscal year and is relying upon an unseasonably strong back half to make its fiscal-year guidance. Furthermore, the new guidance suggests the rate of EPS growth will slow in the back half. While the new CEO may be lowballing the numbers, it seems just as likely that investors attracted by the stock's 9.9 P/E ratio could get burned.

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Fool contributor Cindy Johnson does not own shares of any company named above. 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 has a disclosure policy.