Although we don't believe in timing the market or panicking over market movements, we do like to keep an eye on big changes -- just in case they're material to our investing thesis.

Investors can expect a lower start to the stock market today, as the Dow Jones Industrial Average (^DJI -0.11%) lost 39 points, or 0.24%, in premarket trading. World markets fell overnight, thanks to new manufacturing data out of China and the eurozone that was weaker than expected. Japan's Nikkei index was the biggest daily mover once again, dropping 2% overnight.

Closer to home, today's economic calendar is light. But a fresh reading on the housing market from the National Association of Realtors is expected to show a small slowdown in existing home sales for January when it is released tomorrow at 10 a.m EST. Meanwhile, news is breaking this morning on several stocks that could see heavy trading in today's session, including Wal-Mart (WMT 1.32%), Tesla Motors (TSLA 12.06%), and IMAX (IMAX 1.26%).

Wal-Mart this morning announced soft results for its fiscal fourth quarter. Yes, the retail giant managed to slightly beat earnings expectations, booking profit of $1.60 a share while analysts were expecting $1.59. However, comparable-store sales shrunk in the quarter -- and for the full year, leading to a worse than expected revenue result. The company also offered weak guidance for the coming year, saying that it may not meet its overall profitability goal. Wal-Mart stock is down 2% in premarket trading.

Tesla shares are spiking higher after the company last night booked a record 6,900 Model S deliveries for the fourth quarter. That sales boost helped the electronic vehicle maker double its revenue from the prior year, to more than $615 million. Tesla's gross margin also climbed to 25%, which powered a significant reduction in quarterly losses, to $0.13 versus $0.62 per share a year ago. In a conference call with analysts after the announcement, CEO Elon Musk said demand for the new Model X, set for delivery next year, is already building despite zero marketing for the crossover. "It's like the fish are jumping in the boat," he said. Tesla's stock is up 12% in premarket trading.

Finally, IMAX today booked a 91% boost in per-share profit to $0.44 for the fourth quarter. Sales, at $105 million, came in solidly ahead of Wall Street's expectations as well. Big theatrical hits like Gravity and The Hobbit: The Desolation of Smaug helped power a record box office quarter for IMAX, but investors should be even more optimistic about the company's 277 new theater signings in 2013, which was double the prior year's pace. IMAX's stock is up 12.5% in premarket trading.