Abstract: A pen-based calculator, wherein the user is presented with a screen and a gesture based input device by means of which a sum can be “handwritten” and displayed on the screen. The visibility on the screen of the system's status is provided through two types of feedback: annotation and morphing. As the user is writing the expression, the system can process in the background and, as a symbol is recognised, the user is made aware of this recognition by visual feedback: a typeset character stretched to the stroke's hull replaces the written strokes. Morphing formats the entered expression into a correctly typeset equation by moving the symbols as little as possible from the user's writing, and the morph provides the continuity between the user's input and the typeset equation that allows them to continue to edit and use it. Finally, the answer may be displayed at the correct location relative to the equation.