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 Calix (NYSE:CALX) dropped more than 30% during intraday trading Wednesday after the communications equipment supplier reported mixed third-quarter results and weak forward guidance.

So what: Quarterly revenue increased 27%, to a record $103.6 million, which translated to adjusted net income of $10.2 million, or $0.20 per share. Analysts, on average, were expecting lower adjusted earnings of $0.14 per share on higher sales of $104.35 million.

What's more, Calix stated that while spending from its tier 2 and tier 3 customers has been strong so far this year, those customers have indicated spending will slow down in the fourth quarter. As a result, management expects Q4 revenue to fall sequentially to a range of $97 million to $103 million, which will result in adjusted earnings per share in the range of $0.03 to $0.08.

By contrast, analysts were calling for fourth-quarter sales of $115.52 million, with earnings of $0.20 per share on the same basis.

Now what: No matter how you slice it, that's a big discrepancy from what investors were hoping for, and doesn't bode well for Calix stock over the short term. Even so, you've got to applaud management for being prudent in its guidance and, next year, Calix should still remain nicely positioned to benefit from the broader rollout of gigabit-speed services.

While I wouldn't be surprised if the stock has more downside over the next few months -- even with shares currently trading at a reasonable 13 times next year's estimated earnings -- I think investors would do well to at least add Calix to their watchlists.

Fool contributor Steve Symington has no position in any stocks mentioned. The Motley Fool has no position in any of the stocks mentioned. 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 has a disclosure policy.