Education and demonstration – Mathematics – Arithmetic
Patent
1989-03-06
1990-04-10
Grieb, William H.
Education and demonstration
Mathematics
Arithmetic
434199, 434205, G09B 1902
Patent
active
049156349
ABSTRACT:
A teaching aid includes a plurality of lenses arranged in an array and mounted within a frame member. A slide channel is disposed along the edges of the frame and is imprinted along one edge with numbers from one to ten. A panel having an index mark is slidably disposed in the slide channels and is movable with respect to the lenses to uncover a specified number of lenses equal to the number disposed in alignment with the indicator mark. Each of the lenses has a cross-section providing a wide field of vision.
REFERENCES:
patent: 1941733 (1934-01-01), Badanes
patent: 3172599 (1965-03-01), Passerimi
patent: 3245745 (1966-04-01), Hancock
patent: 3289326 (1966-12-01), Bender
patent: 3435541 (1969-04-01), Tacey
patent: 4241522 (1980-12-01), Jablonski
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