http://en.wikipedia.org/wiki/Hyperinflation#Models_of_hyperinflationBy late 1923, the Weimar Republic of Germany was issuing fifty-million-mark banknotes and postage stamps with a face value of fifty billion marks. The highest value banknote issued by the Weimar government's Reichsbank had a face value of 100 Billion marks (100,000,000,000,000 or One Hundred Trillion US/UK) <1> (
http://www.sammler.com/coins/inflation.htm). One of the firms printing these notes submitted an invoice for the work to the Reichsbank for 32,776,899,763,734,490,417.05 (3.28×1019, or 33 quintillion) Marks.
The largest denomination banknote ever officially issued for circulation was in 1946 by the Hungarian National Bank for the amount of 100 quintillion Pengő (100,000,000,000,000,000,000, or 1.0 × 1020). image (
http://bankjegy.szabadsagharcos.org/xxcentury/p136.htm) (There was even a banknote worth 10 times more, i.e. 1.0 × 1021 Pengő, printed, but not issued image (
http://bankjegy.szabadsagharcos.org/xxcentury/p137.htm).) The Post-WWII hyperinflation of Hungary holds the record for the most extreme monthly inflation rate ever - 41,900,000,000,000,000% (4.19 × 1016%) for July, 1946.
One way to avoid the use of large numbers is by declaring a new unit of currency (so, instead of 10,000,000,000 Dollars, a bank might set 1 New Dollar = 1,000,000,000 old Dollars, so the new note would read "10 New Dollars".) While this does not lessen actual value of a currency, it is called revaluation.