A graphic data-acquisition system which employs an active tracking system provides a retrofittable apparatus for converting a substantially planar surface into an electronic data capture device, in which the components of the system are readily retrofittable, at relatively low cost, to a wide variety of otherwise conventional writing-surface structures, such as so-called dry-erase whiteboards. Conventional triangulation techniques are used to track the position and motion of a writer or eraser. An encoding facility associated with the writing implement provides the ability to distinguish whether the writing implement is used for marking or an as erasing implement, as well as determining the nature or character of written line width or eraser swath. A data stream thus generated can be used in a variety of ways, such as for example, to feed information into the memory of a digital computer, and/or to feed information for transmission to remote stations.