We describe a software tool for performing automatically veri ed arithmetic operations on independent operands when the operands are intervals, or probability distribution functions, or one operand is an interval and the other is a distribution. Intervals and distributions are expressed using the same technique, so the algorithms do not need to distinguish between intervals and distributions in their operation. The tool can calculate common arithmetic operations with guaranteed results (as well as con dence limits on a distribution if the distribution is empirically estimated from samples). A previous paper (Berleant 1993 ) discusses the concepts, algorithms, and related work. Here we emphasize a software tool that implements the algorithms, interacts with the user via a graphical user interface, and saves, retrieves, and prints the results of its calculations.