Swiss watch exports are mired in the longest slump since monthly records began in 1988 after lower shipments to Hong Kong led a decline in September. Exports dropped 5.7 percent to 1.7 billion francs ($1.7 billion), the Federation of the Swiss Watch Industry said in a statement Thursday. The downturn entered its 15th month, making it even longer than the slide after the 2008 financial crisis. “We’re seeing export data flatten out, but there’s no trend reversal apparent,” said Alessandro Migliorini, an analyst at Mirabaud Securities LLP. “Hong Kong is very weak.” The Swiss watch industry is grappling with some of its toughest times since the quartz crisis of the 1970s and 1980s, when battery-powered watches threatened to make mechanical timepieces obsolete. A drop in Asian tourism to Europe has added to a laundry list of challenges including the strong franc and a four-year anti-graft campaign by the Chinese government. For the second month this year, Swiss watch exports to the U.S. exceeded those to Hong Kong, which had been the biggest market for the timepieces for almost a decade.