Geometrical instruments – Straightedge type – Rules
Patent
1984-08-28
1985-07-30
Little, Willis
Geometrical instruments
Straightedge type
Rules
33488, B43L 700
Patent
active
045313032
ABSTRACT:
A drafting instrument includes a plurality of transparent prism arrays, each array including a plurality of transparent prisms juxtaposed in parallel relation and fixed at a predetermined angular relation to a straightedge on top of which the bases of the prisms rest. The preferred predetermined angular relations are: 30.degree., 45.degree. and parallel, to the straightedge. When viewed through the prism arrays, portions of lines not perpendicular thereto, appear offset, providing a way to establish perpendicularity and specific alignment between line and straightedge by re-orientation of the drafting instrument. The straightedge is made substantially thicker than required for structural strength, to enhance the offset appearance of lines viewed through the prism and thus increase sensitivity of offset indication. The straightedge preferably has two edges on opposite sides and parallel with each other. In the preferred construction the prisms and straightedge are made as a unit and protected by a transparent cover.
REFERENCES:
patent: 1800452 (1931-04-01), Karnasch
patent: 1907873 (1933-05-01), Richards et al.
patent: 2248758 (1941-07-01), Higgonnet et al.
patent: 2547745 (1951-04-01), Cade et al.
patent: 2799938 (1957-07-01), Anderson
patent: 2908081 (1959-10-01), Burke, Jr.
patent: 3393034 (1978-07-01), Imai
Little Willis
McClellan, Sr. John F.
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