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 had terrific momentum so far in September, with seven straight sessions of gains bringing the month-to-date return for the S&P 500 (^GSPC -0.88%) to 3.4%. This morning, the indexes are roughly unchanged: The S&P 500 and the narrower, price-weighted Dow Jones Industrial Average (^DJI 0.56%) have moved less than 0.1% each as of 10:05 a.m. EDT.

Southeastern Asset Management has become the largest external holder of media group News Corporation's (NWS -0.12%) voting shares, with an 11.9% position (the Murdoch family has 39.4% of the votes). The company is newly spun off from the Murdoch empire's entertainments assets, which are now housed under Twenty-First Century Fox, as a result of a phone-hacking scandal.

The Financial Times notes that Southeastern disclosed its position on a form reserved for passive investors, which suggests it does not intend to agitate for change. However, the value manager has shown itself willing to take on a more active role in specific situations in the past, including at Chesapeake Energy, where it had a hand in the removal of CEO Aubrey McClendon.

Not all of the fund manager's campaigns have been successful, however. In fact, the board of PC maker Dell looks set to finalize a Southeastern defeat today with a shareholder vote approving a going-private transaction by Michael Dell and Silver Lake. Southeastern and Carl Icahn believe the acquisition undervalues the company and had put together a rival proposal. Nevertheless, Southeastern is an old-school value boutique, so value-oriented investors may wish to kick the tires of News Corporation on the basis of the fund manager's interest.