Abstract: A transmitter device is disclosed for use with a conventional pen in which the ultrasound transmitter is a cylindrical element lying coaxial with the pen and adjacent to its tip, and a jointed eraser structure. Conventional triangulation techniques are used to track the position and motion of a writer or eraser. An encoding facility associated with the pen provides the ability to distinguish whether the pen 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.