# Using A Protractor: An Introduction

## Do you know how to use a protractor? Find out how to easily use this measuring device with these tips and instructions.

The complex protractor was invented in the year 1801 by Captain Joseph Huddart, a United States naval officer. It had moving pieces. The simple protractor is most often used today. Usually, this device is made of clear plastic, and it looks like a half of a full circle; it's an arc with a flat bottom. The inside of the protractor is hollow. Around its arc are degree marks from zero to one hundred and eighty. There are two lines of marks, one on top of the other. The top line is progressive from zero, while the bottom line is descending from one hundred and eighty. There are two lines of numbers so that an angle can be measured from either side.

Along the very bottom is a straight ruler that measures in inches. In the middle is a small hole. Above it, inside the hollow part, is a straight line that measures centimeters.

The protractor is used to measure acute, obtuse, and reflex angles. To explain this further, an acute angle is less than ninety degrees. An obtuse angle is measures between ninety and one hundred and eighty degrees. And a reflex angle is the outer part of an acute or obtuse angle. A protractor is used by map makers, architects, draftsmen, students, and anyone else who needs to measure or draw an exact angle. It's also used to draw angles.

By looking at this measuring device, you can readily see that a half of a circle is one hundred and eighty degrees. Therefore, a complete circle is three hundred and sixty degrees.

To properly use a protractor, let's say that you want to draw a ninety degree angle. This type of angle resembles the letter L. Place the device on a sheet of paper. Make a mark at the small hole in the ruler part. Then, look for the ninety degree mark. It will be directly above the hole. Make a mark there too.

The next step is to draw a line, using the straight ruler, from the small hole to the right edge of the protractor. Finally, move the device so that the edge of the straight ruler connects the two marks you have made. Draw a line to connect the two marks. When you remove the protractor, you will see that you have created a ninety degree angle.

To measure the exact degree of an angle, you must first look at it. If it's more than ninety degrees, or larger than a right angle, then you'll need to follow the set of numbers that are greater than ninety. On the other hand, if the angle is less than ninety degrees, then you must use the numbers that are less than ninety.

Now that you know what set of numbers to use, position the protractor on top of the angle you want to measure. Make sure that the center of the device is on the vertex, which is the place where the two sides intersect. The side of the angle will be visible through the clear part of the protractor. Read the degree mark at the end of the side, and that will be the degrees of the angle.