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.

Stocks are struggling to hold onto gains today, but the Dow Jones Industrial Average  (^DJI 0.62%)this afternoon has fought back from an early loss. As of 2:30 p.m. EST, the Dow has gained around 14 points, and rising blue-chip stocks are just edging the number of companies in the red. 3M (MMM 0.79%) has given the average a welcome lift in climbing 0.74% and ranking among the Dow's daily leaders. However, the index is getting no help from Merck (MRK -0.94%), which has fallen flat after a so-so earnings report released this morning. Let's catch up on what you need to know.

3M's buyback delights Wall Street
3M yesterday announced a huge stock buyback for up to $12 billion worth of shares. The company announced a $7.5 billion plan a year ago, but the new initiative will replace the earlier repurchasing plan. While 3M hasn't said how much was left on the previous buyback, investors have been excited by the news so far, as 3M looks to sustain the momentum that has propelled its stock to among the top 10 performers on the Dow Jones over the past year.

But is now the best time for a buyback from this consumer conglomerate? 3M posted well-received results from its fourth quarter, but the company's organic sales only grew 3.4% for that time, a figure that fell below Wall Street's predictions. While 3M will never be a growth stock for the ages, the company is investing in new markets such as Latin America and Asia in order to tap into developing economies in a bid to overcome the world economy's sluggishness. Investors should be rightly happy about 3M's efforts to keep its stock price high, but the company will need to keep driving growth across its many businesses as the global economy's comeback continues.

Over in health care, Merck's stock has stumbled around the breakeven point today after the drugmaker announced fourth-quarter earnings before the opening bell. The company's quarterly net income dropped from $0.30 per share a year ago to $0.26 in this past quarter, and Merck's profit adjusted for one-time items still missed analyst expectations in coming in at $0.88 per share. Merck's revenue fell 4%, continuing the recent trend across Big Pharma of falling sales as leading drugmakers look to unlock new sources of revenue.

Perhaps most alarmingly, Merck's top-selling diabetes duo of Janumet and Januvia still haven't been able to reignite reasonable growth. Januvia's sales fell a further 1% for the fourth quarter, though combined with Janumet, Merck's total diabetes segment grew 2% in revenue. Januvia and Janumet are key drugs in Merck's portfolio -- the two generated $1.6 billion in sales for the quarter -- and the company has to find a route to spark their growth while it waits on ballyhooed pipeline candidates such as cancer therapy MK-3475. If Januvia and Janumet continue to limp through 2014, it'll be a tough year for Merck investors.