Abstract: A system and method for calibrating and monitoring the height of an electromagnetic radiation expanse above a writing surface is described. An electromagnetic-radiation-generating structure is disposed adjacent produce an expanse of radiation in a substantially planar zone near the writing surface. At least one object is located at a first point in the zone remote from the structure. The object is capable of interacting with the expanse to effect the production of quantitative data correlating to the relative distance between the expanse and the writing surface at the first point. A processor receives and processes the data and allows the position of the expanse relative to the writing surface to be monitored. In a preferred embodiment, four calibration strips are placed near the corners of a writing surface in a system employing two beam-generating scanners to provide X, Y and Z information concerning the location of a writing implement relative to a writing surface.

Abstract: A system and method for detecting movement of an object along an axis normal to a planar surface is described. The invention is applied to a graphic data-acquisition system in which a digitized record is produced according to the X, Y and Z location of a writing implement relative to a writing surface. An expanse of electromagnetic radiation is generated in a zone closely adjacent to the writing surface. An electromagnetic-interactive structure is associated with the writing implement at a location where it will interact with the expanse when the pen is in a write mode. The configuration of the radiation-interactive structure and its positioning relative to the expanse allows the production of an analog data stream which may be correlated to relative distance between the tip of the pen and the writing surface. After fine analog data is digitized, a processing routine is used to determine reliably and accurately when the pen has moved to the non-write mode.