# How To Find Angles Using a Protractor

17th century sailors have been credited or acknowledged as the originators of the ever-indispensable protractor. There was an urgent need for them to plot or chart their nautical courses using their maps. Their design was basic. They made something that was half-circular. The outside edge, or the curved section, of the half-circular material had an arc. That arc contained precise degree markings. They placed the straight edge of the half-circular piece consistent with the specific lines they wanted to measure. And then, they referred to the number of degrees identified by the second line where the arc crossed.

The original protractor is closely similar to the present protractor. Like the original intention, it is still being used as a measuring device. But not, the use of the protractor is being introduced to children early in their elementary or mid school levels. The use of protractor is now focused in knowing the size of an angle and is important in teaching major lessons in mathematics and it is no longer limited in determining nautical notches.

Here are two detailed sets of instructions on how you can effectively find angles using a protractor:

1. Be familiar with the typical protractor. The most common protractor is a semi-circle shape. However, it is also available in various shapes and sizes. Since the protractor is set to measure angles, it has precise markings between 0 and 180 degrees. Since it is generally shaped in semi-circle, it means that a complete circle has 360 degrees. You may also avail of a protractor that has a dual scale. It allows you to measure the angles conveniently, whether your circle opens to the left or to the right. Generally, a reliable protractor can help determine the exact angle between two lines that are intersecting.

2. Use the protractor properly. Start by placing its origin on the angle you wish to measure. Find its vertex and firmly fix it there.

The origin is frequently marked. It has either a crosshair or a very small hole. If it is semi-circle or rectangular, you can readily see the marking at the bottom of the protractor. If it is full-circle or square, spot it just at the center.

Meanwhile, vertex is a common term in your geometry and trigonometry classes. It refers to the actual figure formed by the two rays that share or intersect. It is, in essence, a common endpoint.

If everything is set, keep aligning the baseline of your protractor with one of the two lines that you want to measure. Again, just stay on the vertex’s origin. Then, you can check where the baseline leads you. It is connected to the 0 degree mark and it is indicated on your protractor. After that, you can prepare to note the number where the second line crosses. You have properly marked the angles.

Note that reading a dual-scale protractor may confuse you a bit. It has two scales: inner and outer. The inner scale prompts you to measure from left to right. On the other hand, the outer scale, from right to left.