Educational apparatus
United States Patent 2209157
Inventors:
Glunt, Omer M.
Publication Date:
07/23/1940
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Assignee:
BELL TELEPHONE LABOR INC
Primary Class:
Other Classes:
369/53.100, 360/89, 2/339
International Classes:
G09B5/04; G11B5/00; G09B5/00