When I visited in Zimbabwe in November 2007, the official exchange rate stood at 30,000, the black market rate at 700,000. When I left a week later, the black market rate had moved to 1,000,000. In January 2008, a cousin of mine visited Zim, she exchanged money at 2,300,000. The rate later went to the billions of course, and don't forget Zimbabwe had a currency reform, after which inflation accelerated even more and rates went to the trillions. In mid 2009, 350 trillion Zimdollars = 1 US$. This later became 350 new Zimdollars, at least on paper, as no one is using Zimdollars any more. Apparently many people still have Zimdollar bank accounts, but these cannot be used any more for any transaction.

Casinos had to become creative, so what they did is to still use old chips and plaques, but they then pretended, e.g. that a Z$ 100 chip was now worth, say, Z$ 100 billion. And a week later it might have been worth a trillion. Some chips and plaques got stickers with "new" denominations. Now, of course, everything is US-dollarized.