How to Use a Geometric Compass

By eHow Education Editor

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A compass is a handy drawing tool to have around. Use it to draw circles, make equal line segments or find the midpoint of a line.

Instructions

Difficulty: Moderately Easy

Things You’ll Need:

  • Geometric Compasses
  • Cardboard Or Magazine
  • Pencil Sharpeners
  • Pencils And Erasers
  • Tacks
  • String
  • Rulers

To Draw a Circle

Step1
Insert a sharp pencil into the holder on the compass.
Step2
Open the compass to the radius desired for your circle. The radius is the distance from the center point of the circle to the outer edge.
Step3
Place the compass point on a piece of paper where you would like the center point of the circle to be.
Step4
Place the point of the pencil on the paper.
Step5
Rotate the compass to mark a circle on the paper with the pencil. Draw without lifting the point of the compass off the paper.

To Draw Equal Line Segments

Step1
Insert a sharp pencil into the holder on the compass.
Step2
Place the point of the compass on one end of the line segment you wish to duplicate.
Step3
Open or close the compass so that the pencil point is even with the other end of the line segment.
Step4
Draw a second line segment using a ruler. Make it a little longer than the segment you are duplicating.
Step5
Place the point of the compass on one end of the segment you have just drawn.
Step6
Draw an arc with the compass that intersects the line segment.
Step7
Erase the part of the line segment that goes beyond the pencil mark. The remaining line segment is equal in length to the line segment you wanted to duplicate.

To Find the Midpoint of a Line Segment

Step1
Insert a sharp pencil into the holder on the compass.
Step2
Place the point of the compass on one end of the line segment.
Step3
Open the compass so that the pencil reaches beyond the midpoint of the line segment.
Step4
Draw one arc above the line segment and another arc below the line segment.
Step5
Keep the compass open to the same setting.
Step6
Place the point of the compass on the other end of the line segment.
Step7
Draw arcs above and below the line segment. These arcs will intersect the first set of arcs you drew.
Step8
Use a ruler to draw a line from the point where the top arcs intersect, through the line segment, to the point where the bottom arcs intersect. The point where this line intersects the original line segment is the midpoint.

Tips & Warnings

  • The diameter of a circle is the distance from one edge, through the center point, to the opposite edge of the circle. It is twice the length of the radius.
  • The wider you set the opening in your compass, the larger your circle will be.
  • Use a piece of string to draw very large circles. Tie a pencil to one end of the string. Use a tack to hold the other end in place. Holding the string taut, use the pencil to draw a large circle.
  • The geometric term for finding the midpoint of a line segment is called "bisecting" the segment.
  • Handle a compass carefully; it has a very sharp point.
  • Place a magazine or a piece of cardboard underneath your paper to prevent the compass point from damaging your desktop.

Comments

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charlesa said

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on 10/5/2006 This is in the wrong catagory, it should not be in hiking and such.

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eHow Article:  How to Use a Geometric Compass

eHow Education Editor

eHow Education Editor

Category: Education

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