Fritz Gartner, Erich Berger: System for testing paper money and the like. Oesterreichische National Bank, Karl F Ross, Herbert Dubno, January 6, 1976: US03930582 (96 worldwide citation)

To test the genuineness and/or condition of dollar bills or other substantially identical papers, one or more thickness gauges are positioned in the path of these papers and determine the deviations, if any, of the thickness of a passing specimen from a predetermined value or from the thickness of a ...

Wolfgang Farber: Paper, especially security paper. Oesterreichische National Bank, Herbert Dubno, March 14, 2000: US06036230 (12 worldwide citation)

The invention relates to paper, in particular a sheet of paper, preferably security paper such as a bank note, check or the like, the paper (1) comprising at least one window (2) therethrough bridged by a transparent film (3), such as a plastics film or a transparent paper.