| 摘要 |
A beam compass including a base having a center pivot pin and a bore, and including a portion extending from the base to a center pivot reference point. An elongated beam member is mounted within the bore such that the base is slidably and revolvably adjustable along the length of the beam member. A pencil or pen guide is carried by an outer end of the beam member for guiding a marking instrument. The guide includes a first portion extending from the beam member to a first reference point. The first portion defines at least one aperture. A marking instrument positioned to project through the aperture will engage a drawing surface. An arc or circle traced by rotating the marking instrument relative to the center pivot on the base will have a radius equal to the distance between the first reference point and the center pivot reference point.
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