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 auto-parts maker Gentex (Nasdaq: GNTX) plunged 15% on Thursday after the company's quarterly sales and guidance disappointed Wall Street.

So what: Gentex's first-quarter EPS managed to meet estimates, but a top-line miss -- $290.7 million versus the consensus of $294 million -- is reinforcing investor fears over slowing growth. In fact, the stock is hitting a new 52-week low on the news and is down nearly 30% year to date.  

Now what: Don't expect the stock to turn anytime soon. Management expects second-quarter sales to grow a respectable 15%, implying a top line of about $280 million, but that was also below Wall Street's view of $287.4 million. Of course, with the stock now trading at a reasonable forward P/E of 14, long-term investors might want to take advantage of this short-term turbulence.  

Interested in more info on Gentex? Add it to your watchlist.