A sensing device for use with a surface, the sensing device including a motion sensor configured to generate movement data indicative of movement of the sensing device relative to the surface, a nib for marking the surface, the nib having associated nib information indicative of at least one surface-marking...http://www.google.es/patents/US6627870?utm_source=gb-gplus-sharePatente US6627870 - Sensing device with interchangeable nibs
