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 power conversion specialist Advanced Energy Industries (Nasdaq: AEIS) have fallen as far as 12.4% below last Friday's closing price in today's intraday action.

So what: The company just reported strong sales but weak earnings in the third quarter, with guidance pointing to more of the same divergence between analyst and management expectations in the fourth quarter. The announcement also pulled rival Power-One (Nasdaq: PWER) into a somewhat smaller but still steep nosedive.

Now what: With both Advanced Energy and Power-One diving, it is clear that the market sees an industrywide slowdown happening. The malaise has not spread with conviction to the solar power industry that these two companies support. Or, you could argue that panel makers from First Solar (Nasdaq: FSLR) to Suntech Power Holdings (NYSE: STP) saw their heavy falls over the last couple of weeks and the power inverter folks are just lagging a little bit behind.

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Fool contributor Anders Bylund holds no position in any of the companies discussed here. First Solar and Suntech Power Holdings are twin Motley Fool Rule Breakers picks. Try any of our Foolish newsletter services free for 30 days. 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.