Although we don't believe in timing the market or panicking over daily movements, we do like to keep an eye on market changes -- just in case they're material to our investing thesis.

Throughout the bull market over the past five years, short-term declines in the Dow Jones Industrials (DJINDICES:^DJI) have almost always led to nearly immediate rebounds as investors rushed in to buy momentary dips. But at least for today, the Dow isn't using that familiar playbook, trading down for a brief period this morning and up just 24 points as of 11 a.m. EST. Sharp gains from Caterpillar (NYSE:CAT) and Merck (NYSE:MRK) were essential to keeping the Dow in the green, given that the S&P 500 and Nasdaq are down on the day.

Caterpillar's earnings report provided key upward momentum for its stock, which soared 5.4%. On its face, the report reflected the tough time Caterpillar has had with its heavy-machinery business, as revenue dropped 10%. Yet net income was much higher than investors had expected, with the company managing to produce earnings growth even after adjusting for one-time items that hurt year-ago earnings figures. The company announced a new $10 billion stock-repurchase program, and CEO Doug Oberhelman said Caterpillar already sees some signs of an improving global economy despite an overall sense that 2014 will be fairly similar to the tough 2013 it had.

Merck jumped 3% as analysts at Morgan Stanley upgraded the drugmaker's stock. The analysts cited the company's efforts to keep costs low as bearing fruit, which has been important in light of the revenue declines that Merck has suffered as a result of its patent-cliff exposure. Moreover, with promising treatments on the cancer front, Merck could produce earnings growth that might make the stock's valuation look inexpensive in hindsight.

Yet from a broader perspective, the big question the Dow faces is whether investors will allow the current pullback to become more than a standard buy-the-dip move. Much will depend on the Federal Reserve this week, as it considers whether to continue to reduce its quantitative easing bond purchases or suspend its tapering program in light of global economic pressures. Nervousness about the financial impacts of such a move likely contributed to the declines in Visa (NYSE:V) and Goldman Sachs (NYSE:GS) today, and they could continue to pose a threat until investors get more comfortable with the direction of monetary policy in 2014 and beyond.