![]() The fourth is 10.4 cm long and marked from 0 to 10.7, with each mark divided into 10 parts. The third is not numbered it is 9 cm (3-17/32 inches) long and divided into 17-1/2 sections, each divided into 10 parts. The second is the same length and marked in the same way but in the opposite direction (right to left). ![]() The first scale is 10.4 cm long (4-1/4 inches) and is marked from 0 to 13, with each mark divided into 10 parts. Each scale is rectangular and beveled on the graduated side. ![]() Two sliding thumbscrews in the trapezoid piece permit four different brass scales to be attached. The trapezoid bears a signature: Crozet's Protractor. The frame is open on the interior except for an extension at the center, to which is screwed a German silver trapezoid with points extending from each side of the base. The protractor is graduated to half-degrees and marked by tens from 0° to 90° to 0° in both the clockwise and counterclockwise directions. Finally, use the bottom edge of the protractor as a straight edge to draw a line between the two points.This German silver semicircular protractor fits (and slides) within a rectangular brass frame. Rotate the protractor and line the bottom edge up between the vertex and the small dot. Now, find the hash mark on the protractor that corresponds with the angle you want to draw, and draw a small dot outside of it. Then, line the bottom edge of the protractor up with the vertex and draw a straight line along it. Draw a small dot in the hole on the protractor to mark the vertex. To draw an angle with a protractor, first place the center point along the bottom edge of the protractor where you want the vertex of the angle to be. If the angle is facing left, use the top row of numbers. If the angle is facing to the right, use the bottom row of numbers on the protractor. Follow the other leg of the angle up to the protractor’s arc to see what number it intersects with and find the degree of the angle. Line up the bottom edge of the protractor with one leg of the angle. To measure angles with a protractor, first place the center point along the bottom edge of the protractor over the vertex of the angle you're measuring. You can use a protractor to measure and draw angles. The 2 measurement scales on the protractor makes this tool handy for measuring angles that open up from either direction.If your ray falls in between 2 whole numbers, like 50° and 60°, just count the lines to find your angle’s exact measurement. Protractors typically label measurements in 10s, but between each number are little lines that represent 1°.Or, line the edge of a piece of paper along the line. If the line doesn’t extend past the protractor’s arc, lengthen it with a ruler.If this angle opened from the left, you’d use the outer scale.We know to use the scale on the inside because the measurements are increasing as you move towards the line and they’re less than 90°. In the above image, the angle opens up to the right and is acute.The number that the ray passes through is your angle’s measurement in degrees. ![]() If your angle is obtuse, use the scale with measurements greater than 90°. If it’s an acute angle, make sure you’re looking at the measurements that are less than 90°. Use the scale measurements that are increasing in the direction that your angle is opening up in. Follow the other ray up to the measurements on the protractor's arc.
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