Protractor with a rotor

Details Protractor with a rotor Protractor with a rotor

1994-02-23

1995-04-25

Will, Thomas B.

Geometrical instruments

Straightedge type

Base attached

33435, 33471, 33562, G01B 524, B43L 1300

Patent

active

054087538

ABSTRACT:
According to the present invention there is provided a protractor including a main body surrounding a circular aperture and having a scale of angular measurements thereon, and a rotary cursor mounted on the main body for rotary movement about the center of the circle of the circular aperture. The rotary cursor includes a part-circular center portion engaged in the circular aperture and rotatable within the aperture, and a radial arm portion extending radially outwardly from the center portion to the scale. The center portion of the rotary cursor is generally in the shape of a sector of a circular disc bounded by the reference side edge and the further side edge, and extends through about three quarters of a circle. The arm portion and the center portion of the cursor are formed as an integral unit. The lower main face of the center portion lies in substantially the same plane as the lower main face of the main body whereby when a line is drawn along a reference side edge of the center portion on paper on which the protractor is resting the reference side edge is touching or closely adjacent to the paper to minimize parallax errors.

REFERENCES:
patent: 709219 (1902-09-01), Hochspeier
patent: 923313 (1909-06-01), Anderson
patent: 1062740 (1913-05-01), Sharpe
patent: 1665898 (1928-04-01), Strickland
patent: 2299444 (1942-10-01), Warner
patent: 2480914 (1949-09-01), Gallington et al.
patent: 3059339 (1962-10-01), Danforth

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