How to Read Dial Indicator

Reading a dial indicator means calculating or interpreting the value shown by the scales. The calculation or interpretation results in an easy-to-understand number.

Basically, reading a dial indicator is easy. All you have to do is simply adding the reading value of the inner scale and the outer scale.

Inner Reading + Outer Reading = Total Reading

As the dial indicator parts, the inner scale represents the total revolution of the long pointer. At the same time, the outer scale is the magnification of each division on the inner scale.

Basic Terms to Reading A Dial Indicator

There are several basic things you have to know prior to reading a dial indicator: measuring range, resolution, accuracy, and calibration.

1. Measuring Range

Measuring range defines as the longest distance the dial indicator can measure. Many dial indicators now provide a measuring range of 1″.

2. Resolution

Resolution is the smallest distance that the measuring tool is able to measure. It appears as the smallest division on the scale. Some of them come with a resolution of 0.001″, 0.0005″, and 0.0001″.

3. Accuracy

Accuracy expresses how exactly the same of the measuring result to the standard. It is generally expressed in a “±” sign. Most dial indicators have an accuracy equal to their resolution value.

For example, ±0.0001″. When your indicator has ±0.0001″ accuracy displaying a reading of 0.0007″, then the true value is somewhere between 0.0006″ and 0.0008″. The true reading could be 0.00067 or others yet it will not exceed that range.

4. Divisions

A circular scale is divided into several line-markings. For example, a scale is divided into 100 divisions. The shortest two line-markings are called division. In general, the distance between these shortest two line-markings is the representation of measuring tool resolution.

Most dial indicators’ inner scale is printed with a 10 division scale, at the same time, the outer scale is printed with a 100 division scale.

How to Read A 0.001 Dial Indicator

Most 1″ range dial indicators come with a 10 division inner scale and a 100 division outer scale.

Measuring range divided by the total inner scale divisions is the value of each inner scale division.

1″ : 10 divisions = 0.1″

One inner scale division divided by the total outer scale divisions is the value of each outer scale division.

0.1″ : 100 divisions = 0.001″

This value 0.001″ is equal to the resolution value. You actually don’t need to calculate this because the resolution sign is commonly printed on the dial.

If you start the measurement right from the starting point (0 reading), the steps to get the final reading:

  1. multiply the total inner scale divisions to 0.1″ (for example, 2 divisions, then 2 x 0.1 = 0.2″)
  2. multiply the total outer scale divisions to 0.001″ (for example, 10 divisions, then 10 x 0.001″ = 0.01″)
  3. add those two values of inner scale and outer scale (0.2″ + 0.01″ = 0.21″)

Finally, the reading is 0.21″.

Additional note:

To read more easily, the numerical marking will help you calculate faster. Starrett 25-441J has numerical markings of 0-10-20-30-40-50-60-70-80-90-0 which means an increment of 10. For each increment of 10, there are 10 divisions that represent the reading value of 0.01″. That said, you can easily multiply by 0.01″ for an increment of 10.

How to Read A 0.0005 Dial Indicator

One of the dial indicators that comes with 0.0005 resolution is Mitutoyo 2776S. In this case, it has a 1″ range, 20 inner scale divisions, and 100 outer scale divisions.

Measuring range divided by the total inner scale divisions is the value of each inner scale division.

1″ : 20 divisions = 0.05″

One inner scale division divided by the total outer scale divisions is the value of each outer scale division.

0.05″ : 100 divisions = 0.0005″

This value 0.0005″ is equal to its resolution value. You actually are not required to calculate this value. The resolution sign can be seen commonly printed on the dial.

If you start the measurement right from the starting point (0 reading), the steps to get the final reading:

  1. multiply the total inner scale divisions by 0.05″ (for example, 2 divisions, then 2 x 0.05 = 0.1″)
  2. multiply the total outer scale divisions by 0.0005″ (for example, 10 divisions, then 10 x 0.0005″ = 0.001″)
  3. add those two values of inner scale and outer scale (0.1″ + 0.001″ = 0.101″)

Finally, the reading is 0.101″.

Additional note:

To read more easily, the numerical marking will help you calculate faster. Mitutoyo 2776S has numerical markings 0-5-10-15-20-25-30-35-40-45-0 which means an increment of 5. Each the increment of 5, there are 10 divisions that represent the reading value of 0.001″. That said, you can easily multiply by 0.001″ for an increment of 5.

Pay Attention to the Parallax Error

Since this is a dial scale measuring tool, you have to put attention to the parallax error it potentially posses. Make sure you read the scale upfront the scale, not from the side or top or bottom.

Summary

Learning how to read the dial indicator is easy. You only need to do a little math. Roughly, observe the outer and the inner dial scale, then add those two readings.

Make sure you know the resolution value of your dial indicator. Currently, dial indicators on the market come with a resolution of 0.001″, 0.0005″, and even 0.0001″. The numerical markings also help you interpret the reading.

There are several dial indicator types available. According to the scale it uses, the way of dial indicator reading is basically similar. You need to know the value of each division, etc. However, when reading a test indicator, you may not find them with inner scale. So, it becomes easier.

If this is your first time learning how to read dial indicator, you should learn how to use the dial indicator properly as well. It’s important to get an accurate result.

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