Japan’s Nikkei Stock Average closed down 12.4% on Monday, a historic fall triggered by disappointing U.S. jobs data and a further rise in the yen. The Nikkei's move was the biggest single-day percentage drop since it fell 14.9% in 1987 after the “Black Monday” crash on Wall Street. Nikkei Tumbles After Weak U.S. Jobs DataThe index’s drop followed a 5.8% fall on Friday.