The ``inking'' problems mentioned above are solved by using Electronic Paper (EP) which consists of an integrated display (e.g., a Liquid Crystal Display, LCD) and an XY-digitizer. One of the earliest EP devices consisted of a 12"x12", 1024x1024 pixel plasma device with integrated XY-digitizer . In the case of EP, a non-inking (``untethered'') stylus refill is used for the pen. By providing 'electronic ink', i.e., a trace of legible pixels directly below the pen tip, writers will automatically adapt the exerted force to produce a clean ink path, due to the immediate graphical feedback. Electronic paper currently has a number of other problems, which have mainly to do with the quality of the LCD screen, the writing surface texture, and the parallax problem. The parallax problem refers to the perceived disparity between pen-tip position and ink pixels, due to the thickness of the display glass or plastic cover. Another problem is the friction of the writing surface. Plain glass, for instance would be much to glitchy for normal use, since writers are used to the higher friction of the paper surface. In writing on paper, the friction is assumed to be 4% of the normal force . For this reason, the writing surface on electronic paper is treated to be both non-glaring and have an acceptable friction. Finally, the resolution and image quality of even the best LCD display is incomparable to the high resolution of the ballpoint ink on white paper. A typical dimensioning is 640 pixels over 192 mm. This yields a pixel width of 0.3 mm, which is three times worse than the average whole-field digitizer accuracy (0.1 mm), and 15 times larger than the local digitizer resolution (0.02 mm). Particularly problematic are unlit monochromatic (black & white) LCD screens. At least 64 gray levels are needed, which also allows for anti-aliasing techniques to be used for the graphical inking process. Currently, color TFT versions of electronic paper are appearing, but the relatively high-level signals of the in-screen transistors injects noise into the position sensing apparatus .