Vernier caliper is a measuring instrument used to take measurements of small objects with precision. The instrument has a main scale and a sliding secondary scale. The reading is a combination of the readings on these scales. Hence, it is important to first know how to read these scales before proceeding with the task.

The Vernier scale has been incorporated with various other instruments to take measurements. These instruments are working on different principles, but their readings are taken on the Vernier scale attached with the various instruments. For instance, a polarimeter is an instrument used to measure the plane polarized light. A Vernier scale is attached in this device that will measure the angle of the polarized light. Similarly, a theodolite also has an attached Vernier scale. This instrument is used to measure the angles.

The Vernier scale is used to measure the degrees of rotation by the theodolite. These scales are incorporated with the principles of the various instruments. This article will cover all the various types of Vernier scales attached with the various types of instruments and how these scales are interpreted. The principle of reading a Vernier scale is the same, but the reading interpretation is according to the various instruments.

**Reading a Vernier Scale Measurement on a Linear Scale:**

- First take the reading on the main scale.
- Now take the reading on the secondary scale. This is the division that aligns with the mark on the main scale
- Now add the two measurements to get the final reading.

**Reading a Vernier Scale measurement on a circular Vernier:**

- First take the reading on the main scale.
- Now take the reading on the secondary scale. This is the value of the scale that aligns with the centre line of the main scale.
- Now add the two readings to get the final reading.
- In case of a micromanipulator, the linear scale is read first. Then the rotational scale is read. The rotational scale has 50 increments. Two complete rotations of the rotational scale will be equal to 1.00 mm mark on the linear scale.

**Reading a Vernier scale measurement on the polarimeter:**

- The sample containing the dilute solution of a chiral compound is positioned in a field chamber of the polarimeter.
- The light shield is closed.
- Rotate the Vernier scale until both the halves of the circular display are equal in brightness.
- When the half circle on the right is shaded at 0° then the sample is dextrorotatory (+) and if the left side of the circle is shaded the sample is levorotatory (-).
- In this case, the top scale of the Vernier has a whole number, while the bottom scale will give a decimal number.
- Look for a set of top and bottom tick marks that match perfectly.
- Now read the bottom scale.

**Reading a Vernier Scale measurement on a Theodolite:**

A theodolite is an instrument used to measure the angles. It is used when both the vertical and the horizontal angles need to be measured. It uses a Vernier scale for measurement. The Vernier scale is used for angular measurement. A full circle angle is 360 degrees, while each degree can be divided into 60 minutes.

- The outer scale on the Vernier is fixed, while the inner scale is rotated with the scope of the theodolite. Each marking denotes 30 minutes.
- The top number on the outer scale gives the angle to the right. This will give the angle of the arc that is drawn from the right of the theodolite to the object. The bottom number will measure the complementary arc to the left. The sum of the right and the left angle should always be equal to 360.
- Locate the zero mark on the inner movable scale. Now take the reading where the zero is lying relative to the outer scale. If the zero is lying right on the 130 top scales, then the right angle is 130 degrees.
- Count the minutes.