The user interface is fairly simple. Its purpose is to provide a vehicle for demonstrating the functionality of the calculator without requiring a direct knowledge of the implementation.

The interface itself consists of text prompt at which the user enters expressions using a straightforward expression language. The calculator computes the result and presents the user with a signed decimal stream as output as the computation proceeds and a decimal output when the result has been computed to a user specified output precision.

A version of the calculator which includes the functional operations but only gives output in signed binary form has also been created. This is because in general the functional operations are extremely slow to compute. The signed binary output is more useful because individual decimal digits require four signed binary digits to generate and does not show range of possible values represented by the computed portion of the stream as precisely.

The expression language itself includes decimal numbers, all the basic arithmetic and transcendental functions, the constant , and simple unscoped variables which may be assigned to or evaluated. A graphical representation of the structure of the expression language and a sample session are given in appendix C.