# What is an angle?

When you think of the word “angle”, you may remember the semicircular protractor that used in elementary school days.

The word "angle" is defined as follows in a general dictionary.

1. The size of the angle created by the intersection of two straight lines and planes. The units are radians, degrees, minutes, and seconds.
2. Direction to see things. Also, a position to think about things, "Shoot at different angles" "Consider from all angles"

Source: Digital Daijisen (Shogakukan Inc.)

Here, we will explain about "1." which defines the meaning in physical measurement.
In general life, angles are often used up to "degrees".
However, in industrial measurement, it is used up to "minutes, seconds".
Details are described below.

1 degree: 1/360 angle of the circumference
1 minute: 1/60 angle of 1 degree
1 second: 1/60 angle of 1 minute

However, if the unit is smaller than a minute, it will be very difficult to read the value visually.
There are many ways to measure an angle.
The typical ones are as follows.

1. Semicircular Protractor

The merit of measuring with a protractor is “easiness”.  However, since the measurement is done visually, it is impossible to measure a value smaller than a minute.

1. Protractor

A protractor is a measuring instrument that measures an angle by applying a metal semicircular protractor part and a ruler part to the measurement target.
Though there is a digital display protractor, the accuracy is limited to about 1/4 degree because it is just a hand tool used at the DIY level.  In addition, it is not suitable for measuring small objects because it is measured in contact with the target.

1. Autocollimator

An autocollimator is a measuring device that applies a laser beam to a target, receives the reflected light beam with a camera, and measures the tilt of the object from the light receiving position without contact.
The autocollimator used visually can measure angles up to 0.5 minutes (0.15 mrad), and the electronically controlled autocollimator can measure up to 100 times the visual one.
Furthermore, you can measure very small substances because it can be measured without contact.
However, since measurement cannot be performed without reflecting light rays, it is necessary to either reflect the substance itself or install a reflective object such as a mirror on the target.
It is usually used mainly for adjusting the position of parts and measuring distortion in optical and mechanical systems.

Since its establishment (1995), we have been manufacturing and selling "3. Autocollimator" type measuring equipment / autocollimator.
There are displacement meters in the world that measure length (displacement) in a non-contact manner, but if the object is small, it is difficult to convert it to an angle unless the displacement resolution is high.
Our autocollimator can measure the angle of an object, even if the object is about 1 mm.