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.

What: Shares of equipment rental company United Rentals (NYSE: URI) jumped as much as 11.4% this morning on about double the average trading volume.

So what: United Rentals' second quarter wasn't terribly impressive, as the company missed Wall Street expectations on both the top and bottom lines. That would normally send a stock plunging rather than soaring, but profit margins are improving and management talked up the second-half prospects convincingly enough to light a fire under the stock.

Now what: The company is optimizing its customer mix and fleet expansions to "create demand for our equipment now and in the long term," all as part of a plan to remove United Rentals from the weak and unpredictable construction market. Moreover, management is tapping into low-interest financial markets by selling $500 million of new debt notes this week. Despite United Rentals' claims of controlling its own fate in spite of a soft market, investors are taking this report as a positive sign for construction specialists: Rival RSC Holdings (NYSE: RRR) rose nearly 5% on the news while equipment builder Manitowoc (NYSE: MTW), and even mighty Caterpillar (NYSE: CAT), are posting modest gains on a generally down market day.

Interested in more info on United Rentals? Add it to your watchlist.