Foreign money exchange is one of the fields we can see how rounding error and floating point number works. As currency conversion directs from one currency to another and vice versa, it involves reciprocal of the currency rate (for example, while 1 EUR = 1.47310 US Dollar, 1 US Dollar = 1/1.47310 EUR = 0.67884 EUR), and there exists explicit rounding error when the real conversion occurs (there is no 1.001 dollar. there is only 1.00 dollar or 1.01 dollar).

The article shows an interesting aspect of currency conversion, that a small amount of money suddenly appears from or disappears to nowhere. It used conversion between BEF(Belgium Franc) and EUR, when 1 EUR = 39.5225 BEF.

The table below shows the result of the rounding error in conversion from BEF to EUR. Each of 1, 2, 3, 4, 5 BEF was converted to EUR, and error caused by rounding error is presented.

BEF quasi-exact amount in EUR EUR after rounding Difference Percentage of difference
1 0,025302043 0,03 0,004698 16%
2 0,050604086 0,05 -0,0006 -1%
3 0,075906129 0,08 0,004094 5%
4 0,101208173 0,10 -0.00121 -1%
5 0,126510216 0,13 0,00349 3%

Reference
main article - http://ta.twi.tudelft.nl/users/vuik/wi211/disasters.html#euro
currency converter - http://www.xe.com/ucc/convert.cgi