Due to inflation, 550,000 Zimbabwean Dollars were worth 1 USD in July 2006. At which time they cut three zeros and released the Second Zimbabwean Dollar at a rate of 1000:1.
So 550 Second Zimbabwean Dollars were equal 1 USD in August 2006. Inevitably the Second Zimbabwean Dollar devalued too, until in July 2008 758,530,000,000 second dollars were worth 1 USD. They then cut further 10 zeros off the currency to release the Third Zimbabwean Dollar (10,000,000,000:1). In August 2008 1,780 third dollars were worth 1 USD.
Third Dollar devalued too through 2008, and eventually reached an exchange rate of 300,000,000,000,000 third dollars for 1 USD. In February 2009 further twelve zeros were cut (1,000,000,000,000:1) to create the Fourth Zimbabwean Dollar.
Fourth Zimbabwean Dollar quickly devalued to 150,000 dollars for 1 USD, until it was suspended just two months later in April 2009. Zimbabweans now use foreign currency.
Let's put all those zeros back on, and adjust for inflation.
One US dollar is equal to this many original Zimbabwe dollars:
1,500,000,000,000,000,000,000,000,000,000