Shares of Nippon Sheet Glass Co, the world's largest maker of car windows, plunged by the most in 6y after the company reported an unexpected Q4 loss stemming from its acquisition of UK-based Pilkington Plc. The shares fell by the Tokyo Stock Exchange's maximum of 100 yen, or 15%, to 573 yen, wiping out 67BN yen ($550M) in market value at Tokyo-based Nippon Sheet Glass. It was the biggest drop in Japan's Topix index of 1,730 companies. The surprise 13.2BN-yen loss follows last year's purchase of Pilkington, acquired to help Nippon cut its reliance on TV/computer screens & compete in auto glass against Japan's Asahi Glass. Profit was eroded after Nippon Sheet doubled writedowns at the UK company & set aside £350M for possible fines at the unit. "The earnings revision is a negative surprise," said Norihide Tsuji, analyst at Shinko Securities Co. in Tokyo. Buying Pilkington more than doubled sales at NSG, adding plants in 24 countries & enabling it to compete with Asahi Glass in serving Toyota Motor Co & other carmakers as they press for global supply contracts for windshields & other auto parts. Nippon Sheet had a net loss of 13.2BN yen in the 3m ended March, compared with a forecast for net income of 1.8BN yen, the company said 22/May after markets closed. That cut full-year profit to 15BN yen instead of the 30BN expected. Sales remained unchanged at 680BN yen. Nippon Sheet is scheduled to announce detailed earnings on May 31.