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: Told you so. Two months ago, I took a look at lithium play Rockwood Holdings (NYSE: ROC) at the very top of its 52-week high stock price -- and pronounced the stock still undervalued and likely to go higher. This morning it did just that -- up 10% in response to boffo first-quarter earnings.

So what: Expected to earn $0.61 per share in Q1, Rockwood delivered a true whopper of an earnings beat -- $0.88 per share, or 44% better than predicted. In case you're counting, that makes seven straight earnings beats for Rockwood (and counting.)

Now what: In making my bullish call on Rockwood, I looked past the company's seemingly high P/E ratio and pointed to the firm's strong underlying free cash flow as the true measure of its value. Now that we have new data, let's run it through the number cruncher and see what comes out:

Free cash flow for the last 12 months now totals $283 million -- a number not far off from what we saw two months ago. So while it's true that Rockwood costs more today than it did back then, I still see value in the shares. Basically, we're looking at a 15 times FCF stock today, pegged for superfast 34% growth by Wall Street analysts. This being the case, I still see room for the shares to rise. My advice: Count your winnings ... then buy more.

Maybe Rich was lucky, recommending a high-flying stock at the top of its perigee in February -- but is it tempting fate to double down on that bet after a 25% gain? Add Rockwood Holdings to your watchlist, and watch how this plays out.

Fool contributor Rich Smith does not own (or short) shares of Rockwood Holdings. The Motley Fool has a disclosure policy.

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