Abstract: Interactive printed material and sensor apparatus for use therewith is described. The sensor responds to characteristics of printing on the printed material, for example the degree of infrared reflectance or absorption. The printed material has intelligible components and non-intelligible components. By configuring the printed material and/or the internal programming in the sensor device appropriately, the sensor device can be calibrated to the printed material automatically as the sensor device is applied to the printed material as part of a structured intellectually mediated interaction between the two. In one example, the sensor device is run across a sequence of pre-printed areas specifically designed to enable the values of the property to be presented in a specific order enabling sophisticated calibration and programming functions to be implemented.

Abstract: Apparatus having a sensor unit, preferably in the form of a sensor pen, and printed material is described where the two interact in a wide variety of ways. In particular, the printing on the printed material is configured to have different properties, where the difference is not discernible to the naked eye, for example differences in infrared absorption. A variety of arrangements are described, for example for use in early learning activities, and for testing and revision activities using multi-choice question papers. By using good design engineering, the number of different types of reaction from the printed material that the sensor unit can discriminate between may be as many as several tens, or even more than 100.