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.

Following three straight days of declines, U.S. stocks opened higher on Tuesday, with the S&P 500 and the narrower Dow Jones Industrial Average (DJINDICES:^DJI)both up 0.56% at 10:15 a.m. EST. Earnings season continues, with two technology stocks figuring prominently on the market's dashboard today: Apple (NASDAQ:AAPL) and Yahoo! (NASDAQ:YHOO).

The world's most valuable company, Apple, reported its fiscal first-quarter results after yesterday's market close. Although the company came in ahead of Wall Street's forecasts on revenue and earnings per share, investors pummeled the stock in the after-hours session and they're doing the same this morning, sending Apple down 7.3% at 10:15 a.m. EST. The market is apparently taking exception to iPhone unit sales of 51 million in the quarter (analysts were expecting 55 million), as well as guidance for the second quarter that fell at least $1 short of the $10.93 consensus estimate.

If you think that's bad news, consider that the market's (over)reaction provides patient investors with what looks like an attractive entry point -- as I pointed out yesterday, this morning's prices are below Carl Icahn's cost basis on the billion-dollar commitment he made to Apple shares this month.

Yahoo! will report its fourth-quarter results after today's market close, providing investors with some insight into the health of the online advertising market. (Facebook shareholders are waiting -- and watching -- in the wings, as the social networking company reports after tomorrow's market close.)

Although Yahoo! stock doubled last year, the company's share of the digital advertising market slipped from 6.8% to 5.9% in 2013, with Facebook taking its second spot (behind Google). At the Consumer Electronics Show this month, Yahoo! introduced three new ad products intended to arrest that decline. However, it appears that CEO Marissa Mayer's leadership may be at a crossroads (to paraphrase the title of a useful Financial Times slideshow -- sign-up may be required). Yahoo! lost two top lieutenants in the space of a week this month: COO Henrique de Castro, who Mayer had hired away from her former employer, Google, and Editor-in-Chief Jai Singh.

Investors will be looking for reassurance that these departures are not indicative of broader discontent with Mayer's leadership and for more evidence that her turnaround strategy is yielding tangible results.

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Fool contributor Alex Dumortier, CFA has no position in any stocks mentioned; you can follow him on Twitter @longrunreturns. The Motley Fool recommends Apple and Yahoo!. The Motley Fool owns shares of Apple. Try any of our Foolish newsletter services free for 30 days. We Fools may not all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors. The Motley Fool has a disclosure policy.