Title:
Abacus
United States Patent 2530447


Inventors:
Birdsall, Ida E.
Application Number:
US639948A
Publication Date:
11/21/1950
Filing Date:
02/05/1948
Assignee:
Birdsall, Ida E.
Primary Class:
International Classes:
G09B19/02
View Patent Images:
US Patent References:
1605697Educational device1926-11-02
1400887Educational device1921-12-20
0651892N/A1900-06-19
0227159N/A1880-05-04
0037825N/A1863-03-03
Foreign References:
GB189411304A1894-11-10