Electric Questioner (German Wikipedia)

Analysis of information sources in references of the Wikipedia article "Electric Questioner" in German language version.

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Patent US1860895A: Educational apparatus. Angemeldet am 2. Mai 1928, veröffentlicht am 31. Mai 1932, Erfinder: Louis Marx.‌
Patent US1664842A: Educational appliance. Angemeldet am 15. Oktober 1926, veröffentlicht am 3. April 1928, Anmelder: Knapp Electric Corp, Erfinder: Fred G. Yessler.‌