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 stumbling to end the week as the markets barely hold onto gains. The Dow Jones Industrial Average (DJINDICES:^DJI) was down 25 points as of 2:30 p.m. EST, backing off of an early 50-point gain that marked the highest point on an up-and-down day. Blue-chip stocks across the Dow generally are pulling higher, but a few large losers, such as Boeing's (NYSE:BA) 1.1% fall, have slowed down the index's progress. Outside of the Dow, a few major movers are making headway for investors today, including Biogen Idec's (NASDAQ:BIIB) 2.6% gain. What's behind today's market moves? Let's catch up on what you need to know.

Boeing caps off a good week
Boeing is among the Dow's leading laggards on the day despite good news from the company's slumping defense division. Boeing today inked a $3.6 billion deal to sell eight P-8A Poseidon surveillance planes to the Australian military. It's a much-needed boost to Boeing's defense revenue, which have been hit hard by budget cuts and sequestration in the recent past. In its most recent fiscal year, Boeing's military aircraft revenue fell year over year and slipped from 20% of total company sales to just 18%. Operating margin and the division's contractual backlog also slumped in 2013.

The deal marks the end of a good week for Boeing's backlog overall, however. The company earlier this week finalized a deal with SunExpress for 40 of two versions of Boeing's 737 planes with the option to buy 10 more aircraft. Commercial aircraft sales have dominated Boeing's progress in gaining contracts recently and have sparked this stock's big jump over the past year. The company's commercial airplane backlog jumped an incredible 17% in 2013; at the end of the fiscal year, the mark stood at more than $372 billion in orders and options. As long as Boeing can continue raking in new orders for commercial aircraft, investors can afford more modest levels of growth in the company's defense sphere.

Outside of the Dow, Biogen's stock is making up ground today -- but the company's most-hyped new drug, oral multiple sclerosis therapy Tecfidera, has hit a snag. Britain's National Institute for Health and Care Excellence, or NICE, didn't find Tecfidera to be worthy of its hefty annual price tag, turning down the drug in preliminary guidance and asking Biogen for more information.

It's Tecfidera's first real stumble after a standout start to its market life. The drug earned European approval just this month after winning over FDA regulators earlier, and it's already exploded onto the market in a big way with sales of nearly $400 million in its most recent quarter. Overall, Tecfidera's looking at peak annual sales of up to $4 billion down the road.

However, investors shouldn't worry too much about today's ruling from the U.K. price watchdog. While Biogen will have to regroup in the U.K., fellow oral MS drugs such as Sanofi's (NASDAQ:SNY) Aubagio also have struggled to clear NICE in the recent past. Sanofi was hit with a rejection in preliminary guidance over price, but the French pharma giant later negotiated a price cut on the drug with the British regulator to clear the way to the market. Expect something similar from Biogen, and expect Tecfidera to hit British shores sooner rather than later.

This article represents the opinion of the writer, who may disagree with the “official” recommendation position of a Motley Fool premium advisory service. We’re motley! Questioning an investing thesis -- even one of our own -- helps us all think critically about investing and make decisions that help us become smarter, happier, and richer.