Just to explain -
I work with an accounting system where they use Purchasing and Selling Unit of Measure factors that go out 5 decimal points. It's for things like manufacturing where they have multipliers like .00023 (cost of a screw or the like).

Doesn't sound like a lot, but the numbers have to jive -- especially when they go out into the hundreds of thousands of quantity.

- John
PS: Thanks to all that answered!