This category of pen-based input mainly consists of sequentially entered iconic representations. The pen as the input device offers a tremendous advantage over any other form of computer input device. However, there are also some disadvantages as compared to the normal graphical tools like pencil or brush on real paper. The opaque tablet with an inking ballpoint allows for a more or less natural drawing behavior on paper, but the result on the screen can only be seen by looking up to the CRT monitor. The electronic paper solution immediately (see above) reveals the graphical result in screen resolution and color, but here, the use of the pen is not as easy as in the pencil & paper situation. The general phenomenon which is missing is the mechanical effect of producing a trace, i.e., proprioceptively ``feeling the friction'' of the pen-to-surface contact. Two basic principles are worth mentioning: (i) free-style drawing as a process in which pixel ink is deposited in a bitmap, and (ii), free-style drawing as a process in which a position vector is produced in time. The latter type of recording can be played back in time easily. This also allows for a stroke-based ``undo'' operation during the interaction, which is more difficult to achieve in the case of bitmap-oriented drawing.