How to use magnetic protractors

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What is a protractor

A protractor is an instrument used to measure angles, typically in degrees. They are available in semicircle and full-circle designs, with the semicircle being the most common type. A semicircular protractor measures 180 ° while a full circle protractor can measure 360 ​​°. Often times, protractors are clear so you can see your lines and shapes under the gauge as you measure, and they have a series of markings on the outside edges for measuring angles.

Use a protractor to measure an angle

You can measure an angle with a protractor by identifying the vertex or center point of the angle, placing the origin or center point of the protractor over the vertex, aligning the bottom edge with one of the angle edges, and locating the measurement of the angle.

Find the vertex or midpoint of an angle

The vertex of an angle is the intersection where two lines meet. Find the two lines and see where they meet. If the two lines of the angle don't touch, use the straight part of the protractor to extend the lines until they meet to find the vertex.

Place the protractor origin over the vertex

Find the origin near the straight edge of the protractor and in the center. Usually there is a hole or circle marking the origin with vertical and horizontal crosshairs to perfectly align the origin at the vertex. Align the horizontal edge of the origin with one of the edges of the angle so that the other edge of the angle aligns with the measurements along the curved edge, as shown in the image above.

Find the angle in degrees

Find the acute angle

An acute angle is the smaller angle where one line meets another, or technically any angle smaller than 90 °. When a line meets another line, 2 angles are formed, the acute angle is the smaller one. If the origin of the protractor is aligned over the vertex of the angle and the horizontal edge is aligned with one of the lines, find the marker along the curve where the line meets. If the acute angle is on the left, then the mark is on the outside or outermost edge of the protractor. If the acute angle is on the right, the mark is on the inside of the curve.

There are two rows of marks on a protractor to measure degrees of angle from either the left or the right. The readings should increase in the direction you are measuring.

Find the obtuse angle

An obtuse angle is the larger angle when two lines meet, or technically any angle that is greater than 90 degrees. If one line meets another line, making two angles, the obtuse angle would be the larger angle. If the origin of the protractor is aligned over the vertex of the angle and the horizontal edge is aligned with one of the lines, find the marker along the curve where the line meets. If the obtuse angle is on the left, then the mark is on the outside or outermost edge of the protractor. If the obtuse angle is on the right, the mark is on the inside of the curve.

Source: ruler.