The Dow wavered before it eked out a small gain on Tuesday, enough to match its longest series of gains since February 2011. The S&P 500 and Nasdaq fell, however. Tech heavyweight Apple fell after an analyst said the company has a 25 percent chance of missing its quarterly revenue forecast as iPhone sales slow. Among gainers, Merck rose after the drug maker said a data safety monitoring board recommended that a study of its cholesterol drug Vytorin should continue. Yum Brands gained even as the Pizza Hut and KFC owner said January-February sales in China were smaller than expected following a food scare over its chicken suppliers.