A portable display device capable of presenting a document in an easy to read format, in which a simultaneous display of different parts of the document in reasonable sizes can be made, by a simple operation of the device. The display device comprises a document memory for storing documents to be displayed,...http://www.google.com.tw/patents/US5467102?utm_source=gb-gplus-share專利 US5467102 - Portable display device with at least two display screens controllable collectively or separately
