Reuters
Here's what went down.
Remember that there are two different Chinese currencies - the onshore yuan (CNY) and the offshore yuan (CNH).
Increasingly, the Chinese government has been buying the onshore yuan to keep it from falling too fast.
It wants the yuan to weaken to help boost exports as the country's economy slows. But it also wants to maintain the yuan's stability, spending $108 billion in December to do so.
The offshore yuan, however, is a different story. It floats more freely, and even though the Chinese government can direct big state banks to buy offshore yuan, as they were doing Wednesday, according to The Wall Street Journal, it is more reflective of market sentiment.
On Thursday night, while Americans were sleeping, the spread between the onshore yuan and the offshore yuan widened.
The offshore yuan started to fall in early trading. The onshore yuan, which has been propped up all week by China's central bank, the People's Bank of China, started to fall too.
That sent Chinese stocks wobbling up and down at the open, and the rest is the beginning of what seems to be another global market rout.
We've been watching the yuan lead markets down since the beginning of 2016. Last week an intentional 0.25% depreciation of the onshore yuan sent markets sliding all over the world.
On Thursday, the offshore yuan fell as much as 0.7% against the dollar before stabilizing at a dip of about 0.5%. The onshore yuan fell by about 0.2%.