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 haven't moved much over the past couple of weeks. This afternoon, with the Dow Jones Industrials (DJINDICES:^DJI) down a meager 15 points as of 12:30 p.m. EST, stocks are simply taking a breather after their recent record run-up. Yet while broad-market followers look for signs of general economic strength or weakness, Wal-Mart (NYSE:WMT) will give a key reading on the state of the retail sector when it issues its quarterly earnings report tomorrow. With so many consumer-goods companies relying on Wal-Mart for a substantial portion of their overall sales, investors should look closely at what the retail giant has to say.

Wal-Mart will release its results before the market opens tomorrow. It typically issues a press release detailing earnings results, as well as a pre-recorded phone call in which management reviews the numbers, at about 7 a.m. EST.

Wal-Mart's challenge is that it faces competition on two major fronts. Most investors have focused on the impact of (NASDAQ:AMZN) and online shopping on the big-box retail industry, and Amazon's recent quarterly results showed that it has continued to make an ever-larger impression on shoppers. With Internet commerce accounting for less than a tenth of all retail sales, Amazon has a lot more room to encroach on Wal-Mart and its fellow big-box retailers.

But many investors have played down the size of the competitive threat to Wal-Mart from other big-box retailers. Both Target (NYSE:TGT) and Costco Wholesale (NASDAQ:COST) have made greater inroads toward finding steeper growth trajectories than Wal-Mart. For Costco, the ability to charge highly profitable membership fees has freed the warehouse retailer to slice margins to the bone on the goods it sells, giving customers a value proposition that has led to extremely high renewal rates that create a reliable stream of pure profit for the company. Meanwhile, Target has sought to make itself a more attractive and upscale destination for shoppers, incorporating margin-boosting measures like brand-name designer partnerships to woo customers and create buzz.

Even with sluggish results lately, Wal-Mart remains a key distribution outlet for many consumer-product giants, including several Dow components. The news that Wal-Mart gives investors tomorrow will likely send ripples throughout the Dow, especially if its results point to a weak holiday season that could have disastrous effects on retailers and product manufacturers throughout the industry.