Warren Buffett is officially getting poorer. After just a few months as the second richest man in the world, he has been passed by Mexican telecom billionaire Carlos Slim.

According to Forbes, Slim is worth $53.1 billion and Buffett only $54.2 billion. Slim did it the hard way. He increased his net worth in the stock market. His holdings in Carso Telecom, which controls the large Mexican phone company Telmex, went up 15% and the value of his holding in wireless operator American Movil is up 4%.

The measurement means little. Slim's net worth has almost doubled in a little more than a year. The Mexican stock market is up almost 50% over that period. A slip in the economy there could easily push him back down the list. Buffett's investment in Berkshire Hathaway Inc. (NYSE: BRK..A) and Bill Gates' (No.1 on the Forbes list) holdings in Microsoft Corp. (NASDAQ: MSFT) are certainly less volatile.

Because so many of the fortunes of the people on the Forbes list are based on holdings in public companies, the list could literally be recalculated every day. The magazine may have to do that to keep up with billionaires like Slim.

Douglas A. McIntyre is a partner at 24/7 Wall St.