This class is a container class for numbers with a number of associated 
symmetric and asymmetric errors. It overloads practically all common 
arithmetic operations and trigonometric functions to propagate the errors. 
It can do proper scientific rounding (as explained in more detail below in 
the documentation of the significant_digit() method).

You can use Math::BigFloat objects as the internal representation of 
numbers in order to support arbitrary precision calculations.

Errors are propagated using Gaussian error propagation.

With a notable exception, the test suite covers way over ninety percent of 
the code. The remaining holes are mostly difficult-to-test corner cases 
and sanity tests. The comparison routines are the exception for which 
there will be more extensive tests in a future release.

WWW: http://search.cpan.org/dist/Number-WithError