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 have taken another big dive in the wake of yesterday's fall, as the Dow Jones Industrial Average (DJINDICES:^DJI) has shed all of its earlier gains to nose steeply into the red. As of 2:15 p.m. EST, the Dow has dropped more than 70 points, with only a handful of its member stocks managing to stick it out in the green today.

Fortunately for shareholders, Microsoft (NASDAQ:MSFT) has managed to have a good day so far, with the tech giant's stock gaining 0.5% despite the Dow's gloomy session. Health care is not looking so bright, however: UnitedHealth's (NYSE:UNH) shed 0.5% after the company released some important details regarding its look into the new year. Let's catch up on what you need to know.

Microsoft's entertainment bounce
Microsoft is jumping today as the company's consumer hardware group has rallied behind strong sales of its Xbox One entertainment and gaming console. The company reported that it had sold more than 1 million of the units in its first 24 hours after launch, and that demand remains above supply. Microsoft said it's "selling every Xbox One we can make," a good start for the firm after rival Sony (NYSE:SNE) beat it to the market by launching its competing PlayStation 4 a week ahead of the Xbox One.

It's lining up to be a stiff competition between Microsoft and Sony in this industry's new generation of consoles, as Sony also reported selling more than a million PS4 consoles in the launch window's first 24 hours. Sony also recently updated its sales figures, with more than 2.1 million PS4 devices sold across the globe.

Even with Microsoft's rival performing exceptionally well, however, this big start is huge for the company. Microsoft's consumer hardware division has struggled with the Surface tablet's mixed results. Its consumer hardware branch saw its gross margin decline substantially in the third quarter due to higher costs of revenue from the Surface, and the Xbox One's good start should at least reinvigorate confidence in this area among investors.

Over in health care, UnitedHealth's bad day has come after the company said that Obamacare's initiatives could cost the firm between $0.90 to $1 per share in net earnings in 2014. That's a steep price to pay, confirming suspicions from the company and rivals earlier in the year that the new health-care law could raise costs significantly.

Costs already have been a big problem at UnitedHealth, which saw medical cost growth outpace total revenue growth through the first nine months of 2013, with the former growing 12.3%, and the latter jumping 11.6%. UnitedHealth has made a point of playing cautious with the new law; but with Medicare costs in particular in focus around Obamacare -- UnitedHealth expects cuts to privately funded Medicare to cost it $0.25 per share next year alone -- the company will need to stay careful as it moves into the future of health-care reform.

Fool contributor Dan Carroll has no position in any stocks mentioned. The Motley Fool recommends UnitedHealth Group. The Motley Fool owns shares of Microsoft. 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.