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: Here we go again, folks. Late last month, Global GeoPhysical Services (NYSE: GGS) popped 10% for no particular reason. Today, it's a 10% drop -- again for no reason in particular.

So what: Today's plunge makes a great buying opportunity. Back in April, I said: "The long-term argument in favor of buying this stock remains intact … Global Geo [is] still churning out free cash flow at the rate of $101 million per year. The resulting valuation of 6.4 times FCF tells me there's every reason to buy the stock."

Now what: The stock is now 13% cheaper than when I wrote that pitch. At 5.6 times free cash flow, that makes Global Geo an even better deal than it was last time around.

Want to get more info on Global Geo? Add it to your Watchlist.

Fool contributor Rich Smith does not own (or short) shares of any company named above. 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.