Goniometer

A protractor is a tool for measuring angles.
In the simplest typology it consists of a circle (or a semicircle) with a graduated circumference and a pointer in the centre.

By centering the pointer on the origin of the angle, and making the zero of the graduation coincide with one side, the value of the angle can be detected by reading the position of the other side along the graduated circle.
Office and technical drawing protractors are made of transparent plastic, to facilitate reading the position of the sides through the instrument itself. These, although not very precise, are also inexpensive.
Shop protractors are made of a more robust material, typically stainless steel, to prevent rust from making reading difficult or erasing the scale. Often the surface is matted to prevent glare when reading.

How can you determine an angle on a sheet of paper with a protractor?

1 – draw a line with the set square representing one side of the angle.

2 – place the center of the protractor on the end of the line chosen as the vertex of the angle and the other part of the line passing through the zero of the protractor 

3 – On the graduated scale of the protractor, mark a point on the desired angle.

4 – use the set square to join the vertex point to the point found on the scale.

The two lines will have the desired angle.

Anyone who wishes to contribute to improving this page can post their experience or memory in the comments section.

The content of this page was taken from: https://it.wikipedia.org/wiki/Goniometro