Chinese stocks will decline by about 14 percent over the next three weeks, Tom DeMark said.

Chinese stocks will decline by about 14 percent over the next three weeks as the market demonstrates a trading pattern that mirrors the U.S. crash in 1929, according to Tom DeMark, who predicted the bottom of the Shanghai Composite Index in 2013.

The Shanghai Composite Index will sink to 3,200 after plunging 8.5 percent Monday to 3,725.56 in the worst selloff in eight years, DeMark said. The index’s moves since March are tracking those of the Dow Jones Industrial Average in 1929 when the gauge lost as much as 48 percent, he said in a phone interview for Bloomberg.

“You just cannot manipulate the market. Fundamentals dictate markets.” DeMark said.

DeMark said he’ll reassess the market once the Shanghai index hits 3,200, which would almost wipe out this year’s gain. If that level, which is around the 61.8 percent Fibonacci retracement from the June peak, fails to hold, the market could “unravel” quickly, he said.DeMark said his indicators work best to pick up buy and sell signals when the market is “manipulated.” That is because intervention makes the imbalance in the supply and demand of stocks “more apparent” and easier to identify, he said.

DeMark has provided consulting to hedge funds including George Soros’s Soros Fund Management and Leon Cooperman’s Omega Advisors. His company also sells subscriptions to the indicators on the Bloomberg Professional service.