Abstract: Where a signature is to be automatically verified, or data is to be entered into a computer, a special pen is usually employed but this pen is liable to be stolen or vandalized. In the present invention the tip of an ordinary pen presses lined paper on to a transparent plate and modifies internal reflection in the plate at the point of contact. A light source edge-illuminates the plate and light received by a receiver at another edge of the plate varies in intensity as the pen tip crosses the lines. By measuring the intervals between crossing line boundaries information is obtained which can be analyzed for use in signature verification and data entry.