Patent
Patentdatenbank USA 1990

- Patent:US4900255 13.02.1990 Laghi, Aldo A. : For two-stage Quincunx
- Patent:US4960029 02.10.1990 Nelson, Michael B. : Musical scale determining device
- Patent:US4961362 09.10.1990 David Gunn : Chord key calculator assembly
- Patent:USD308884 26.06.1990 M. Michaelson : Growth Ruler or the like