A shaky day ended in the red with all benchmark indexes sporting modest losses by the end of the day. Stocks seesawed from gains to losses for much of the session ahead of highly anticipated comments from Fed Chair Yellen on Friday. Jewelry chain Tiffany & Co. (TIF) moved lower even after showcasing strong quarterly sales growth. Solid demand for its high-end lines and increased sales of wholesale diamonds helped to drive revenue. Industry peer Signet Jewelers Ltd. (SIG) topped out the S&P 500 after also showing off a better-than-expected second quarter. Wells Fargo reiterated its OUTPERFORM rating after the earnings beat. Apple Inc. (AAPL) will build a billion-dollar data center on 2,000 acres in a suburb near Des Moines, Iowa. The world's largest company will get nearly $208 million in incentives including tax refunds and tax breaks.

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