But shares in Gemstar, which owns 200 patents to onscreen TV guides, have plunged further due to a US ruling in a key patent dispute. The value of a $7.5bn investment in Gemstar by News Corp in July 2000 had shrunk to roughly $850m by last week, a plunge that will force an even larger write-down, say analysts. The company could also face writedowns on assets in Asia and Europe.