How to Use a Protractor?

How to use a protractor?

Table of Contents

Introduction

Precision is key when it comes to measurements. To achieve it, you have to:

1. have a high-quality measuring instrument (it doen’t have to be expensive but it should be made properly so that you can get correct measurements);

2. know how to use and read the instrument.

In this article, we will explain what a protractor is, what protractor types are there and how to use them. In addition, you will learn how to read a protractor.

What is a protractor?

It is a special instrument that is designed to measure angles. Using a protractor, it is easy to know how many degrees there are in an angle. Protractors are irreplaceable in geometry, mechanics, engineering, etc.

A bit of theory

To use a protractor the right way, you have to know a thing or two about angles. Let’s quickly skim through a few things you need to know.

What is an angle?

What is an angle

It is a figure that is formed by 2 rays or lines that share a common endpoint (vertex).

What are the parts of an angle?

An angle consists of the following parts:

1. vertex - the point where 2 arms are met;

2. arms - 2 straight lines that are joined at a vertex.

What are the types of angles?

There are 6 angle types:

What are the types of angles

Now that you know the basics, let’s move on to using a protractor.

How to use a simple semi-circular protractor?

There are various types of protractors. The most common one is a simple semi-circular protractor(or half-circle protractor) that you know from school. This instrument measures angles up to 180 degrees.

Let’s take a look at the elements of a protractor.

elements of a protractor

Typically, there are two scales:

1. an outer scale (or a clockwise degree scale);

2. an inner scale (or a counterclockwise degree scale).

At the bottom of the protractor, there is a base line with a center point (or origin). How is a protractor used? Let’s figure out how a simple half-circle protractor is used.

How to use a protractor to measure angles?

1. Identify by eye, whether your angle is right, acute, or obtuse.

How to use a protractor to measure angles

2. Place the origin (the middle of the protractor’s base line) over the vertex. One arm of the angle should be aligned with the base line of the protractor.

How to use a protractor to measure angles

3. Follow the opposite arm of the angle up to the degree marks on the arc of your protractor. Make sure that the line passes through the arc. The angle’s measurement in degrees corresponds to the number on the arc the line passes through.

How to use a protractor to measure angles

For acute angles (less than 90 degrees), use the inner (counterclockwise) scale. For obtuse angles (more than 90 degrees), use the outer (clockwise) scale.

How to draw an angle using a protractor?

1. Draw a straight horizontal line. It will be one arm of the angle. Use the base line of your protractor.

How to draw an angle using a protractor

2. Place the origin of the protractor at the beginning of the line and mark this place. It will be the vertex of your angle.

How to draw an angle using a protractor

3. On the scale of your protractor, find the degree you need. Draw a mark on the paper there. Remember to use the anticlockwise scale for acute angles & the clockwise scale for obtuse angles.

How to draw an angle using a protractor

4. Draw the other arm of the angle. Using the flat edge of the protractor or a ruler, join the vertex and the marked degree, drawing a straight line.

How to draw an angle using a protractor

Measure the angle you have drawn using a protractor to check whether it was drawn accurately.

How to use a semi-circle bevel protractor?

A semi-circle bevel protractor is essentially a simple protractor with a pivoted arm.

Let’s take a look at its elements.

elements of semi-circle bevel protractor

How is it used?

1. Loosen the set screw & place the object between the protractor and the blade.

How is semi circle bevel protractor used

2. Read the scale. Don’t forget to use the inner scale for acute angles and the outer scale for obtuse angles.

How is semi circle bevel protractor used

How to use a universal bevel protractor?

A universal bevel protractor (also a Vernier (bevel) protractor, or sometimes a universal bevel dial protractor) can be adjusted to fit the angle you want to measure. Unlike a simple protractor we considered earlier in this article, it has a more complicated construction.

Let’s skim through the elements of a universal bevel protractor.

elements of a universal bevel protractor

As with any instrument, it is useful to know its elements so the working principle is easier to understand.

The beam (or base) is a stationary part of the protractor. It is used as the measuring edge.

The blade is an adjustable element that rotates along with your protractor.

The main scale on the bevel protractor is used for measuring angles in degrees (°).

The main scale on the bevel protractor

The Vernier scale measures angles in minutes (′). It is used if you need more accurate readings than the main scale can offer.

The Vernier scale on the bevel protractor

The dial of a universal bevel protractor is graduated from opposite zero marks to 90 degrees each way.

There are models with an attached magnifying glass so it is easier to read the angles.

The swivel plate rotates on the dial.

With this protractor, any angle can be measured.

How to use a universal bevel protractor

Let’s measure an acute angle, using a universal bevel protractor.

1. Unscrew the locking nut that is located on the front part of your protractor. It should be done so that you can swivel the blade.

How to use a universal bevel protractor

2. Place an object the angle of which you want to measure between the beam and the blade of the protractor. The beam and the blade should be pressed against the sides of the object. There should be no gaps. Otherwise, the reading will be incorrect.

How to use a universal bevel protractor

3. Tighten the locking nut.

How to use a universal bevel protractor

4. Take the reading.

If you measure an acute angle (which is our case), the reading may be obtained directly from the scale.

To measure an obtuse angle between the beam and the blade, the number of degrees you see on the scale when measuring the angle should be subtracted from 180 degrees as the dial is graduated from opposite zero marks to 90 degrees each way.

As we can identify by eye that we have an angle that is less that 90 degrees, we have an acute angle, we won’t subtract anything.

First, let’s measure our angle in degrees.

Look at the zero on the Vernier scale (it is located below the main scale). Then, look at the mark on the main scale right above the zero mark on the Vernier scale.

In our case, we have 79 degrees.

How to use a universal bevel protractor

Now that we know the number of degrees, let’s get a more accurate reading and count the number of minutes (in addition to degrees).

Make sure that you read the Vernier scale in the same direction that you read the main scale.

Look at the Vernier scale in a clockwise direction, starting from zero. Count the number of minutes until you reach a minute mark (on the Vernier scale) that matches up exactly to a degree mark (on the main scale). In our example, we have 45 minutes.

So the final reading is 79° 45′.

How to use a universal bevel protractor

How to use a protractor with depth gauge?

A protractor with depth gauge will help you measure both the angle and depth. On the protractor, there are graduations form 0 to 180 degrees in opposite directions so both direct and supplement angles can be read. There is also a ruler that is attached to a protractor using a nut so the ruler can be easily locked at the desirable angle.

Let’s figure out how to use a protractor and depth gauge.

Depth measurement

1. Put your protractor on top of the groove.

How to use a protractor with depth gauge

2. Release the grip of the locking nut in the ruler by loosening it.

How to use a protractor with depth gauge

3. Let the ruler drop into the groove, use the locking nut to ensure that it doesn’t move. For a vertical groove, the ruler should be perpendicular to the protractor.

How to use a protractor with depth gauge

4. Take the depth readings. Look at the place where the scale of the ruler meets the protractor.

How to use a protractor with depth gauge

Angle measurement

1. Place the object against the bottom of your protractor.

How to use a protractor with depth gauge

2. Line the ruler against the other angle side.

How to use a protractor with depth gauge

3. Tighten the locking nut so the ruler doesn’t move.

How to use a protractor with depth gauge

4. Read the angle, using a protractor.

How to use a protractor with depth gauge

How to use a digital protractor?

An electronic protractor (or a digital protractor) measures the angle automatically, there are no scales so the device is easier to use than a regular, non-digital protractor.

You can see an example of an electronic protractor that is similar to a bevel protractor in design. It automatically reads the angle and as with most digital devices, the result is shown on the display.

Digital protractor

There are other designs of digital protractors.

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They resemble a box. To use such a device, you need to place it on the surface of the object and thus you will measure the angle.

To use an electronic protractor, follow a few simple steps:

Horizontal measurement mode

1. Set your protractor to the “horizontal measurement mode” (there may be the ABS symbol on the display).

How to use a digital protractor

2. Put your protractor on an angled surface.

How to use a digital protractor

3. The measurements will be shown on the display.

How to use a digital protractor

Relative measurement mode

If you are working with two angles, follow the steps below:

1. Put your protractor on the 1st angle.

How to use a digital protractor

2. Press the zero button to reset the angle on the display.

How to use a digital protractor

3. Put your protractor on the 2nd angle.

How to use a digital protractor

4. On the display, there will be the angle between the 1st and the 2nd angles.

How to use a digital protractor

Conclusion

After reading this article, we hope that you understand what a protractor is and how to use it. There are different types of protractors, you just need to get the right one that is perfect for your application. Choose from a broad range of protractors on Mega Depot!

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