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 China MediaExpress Holdings (Nasdaq: CCME) plunged more than 12% in early trading and remain down more than 9%, continuing a tenacious tussle between long and short investors.

So what: Traders must love this stock. In the past month alone, shares of China MediaExpress have traded between $10.66 and $17.15 each. Roller coasters have nothing on the stock.

Now what: Such stomach-churning volatility has to make investors nervous. And yet there is a growth story here. China MediaExpress claims the leading position in providing bus-based TV ads to China's up-and-coming consumer class.

Citron Research says management's faking. Wall Street analysts say otherwise, projecting 22.5% annualized profit growth over the next five years, resulting in a nearly microscopic 0.24 PEG ratio. Who do you believe?

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