Working Principle: How A Caliper Works (Vernier, Dial, & Digital Model)

In terms of measuring the distance of the internal-external dimension and diameter of an object, it is a lot harder to do with a conventional measure like a ruler. However, it’s a lot easier with a caliper. There’s a lot to be said for a caliper, but how it actually works? How does it serve to measure that?

To understand the working of the calipers, it is necessary to recognize the body parts. In this case, the part that contributes to how the measurement is taken is the key. That is to say, how the reading is displayed is the point we can observe to study it.

As classified in the previous post, there are two main categories of calipers:

  1. Indirect reading calipers (inside, outside, divider, and odd leg calipers),
  2. Direct reading calipers (vernier, dial, and digital calipers).

Each of them has a different style of working principle that will be exposed. Also, they have a different reading type which is the sign of their different working principle.

How Calipers Work?

Let’s have a look at the working of calipers that belong to different categories:

Indirect Reading Calipers:

1. Inside Caliper

While measuring with an inside caliper, you need to first close the legs of the caliper so that it can fit inside the object easily. Once the legs of the caliper have reached the inside of the object, you open them according to the required measurement. Once you have adjusted the legs properly, you can tighten the caliper and you can remove it from the internal diameter of the object. When the caliper is removed, it is ready to measure with a separate scale.

Here we conclude that the inside caliper basically works manually. It’s truly human work. There is no mechanism that runs automatically.

2. Outside Caliper

The outside caliper works exactly like an inside caliper but the outer of the object is measured. Hence, you adjust the legs according to the widest part of the object and then tighten it. Once you have adjusted the legs properly, you can take the measurement when the outside caliper is removed from the widest part.

Similarly, there is no set of tools that are designed to work in such a way to ease human work. An outside caliper is totally a manual tool.

3. Divider Caliper

This is another conventional caliper that works manually. The divider caliper is just like a compass. The legs of the calipers have sharpened edges, you put the edges of the divider caliper on the points whose distance needs to be measured. You can use a separate scale to measure the distance between the two points.

4. Odd Leg Caliper

The odd leg caliper works the same way as a compass. The bent leg is set on a fixed place while the other leg is used to scribe a line. It’s the same with the three caliper types above.

Direct Reading Calipers:

1. How Does A Vernier Caliper Work?

vernier scale
Vernier Scale

To find the readings of the object using a vernier caliper, make sure to check the zero error by closing the jaws. If the reading is zero then there is no error. Adjust the jaws on the object and then with the help of the lock screw, tighten the jaws and take the readings.

The measurement result is gained through the mechanism of the vernier scale. In other words, a vernier caliper works showing the reading using the vernier scale. How the reading is taken from the movement of every mark that aligns up to the opposite marks. This is a great idea, cheap, reliable, accurate. But you need to have a good sight.

2. How Does A Dial Caliper Work?

Dial calipers work differently compared to vernier calipers. They have a rack and dial scale to show the readout. When it slides, the rack will rotate the gear inside the dial scale, then the needle rotates to pinpoint a certain number.

A dial caliper is easier to read than the vernier caliper. There will be two scales. The second scale is the dial gauge.

3. How Does A Digital Caliper Work?

Digital Caliper

Although manual calipers are preferred over digital calipers due to being less expensive and do not require batteries for operation, digital calipers are easier to read and can easily switch between metric and imperial readings just with a press of a button.

The incorporation of multi-plate capacitive sensors achieves this cost efficiency.

Digital calipers employ numerous plates to build a capacitive array capable of correctly sensing motion. A digital caliper has a stator and slider (“rotor”) plates. The stator is inserted in the metallic ruler that holds the electronic enclosure. The slider is housed in the electrical casing. The stator design is created on the top copper layer of a conventional glass-epoxy laminate and attached to the caliper’s stainless-steel bar. To establish the direction of motion, separate sin and cos angles are required. With the typical PC fabrication approach, the combination of plate-counting digital circuits and analog interpolation between plate gives 0.0002” over 6. The application uses a small watch battery to demonstrate the micro amp-level current usage made feasible by technology.

As a result, these measurements are only achievable because of a sequence of capacitance sensors that span the length of the beam. As a result of the change in electrical charge sensation sensed when the distance between the jaw changes, measurements are then taken. Because of the rectangular plates engraved on the copper plate are present beneath the slider scale, when the sliding jaw moves along the main scale, the capacitance, which is the electrical charge between the plates, changes, sending a signal to the chip within the caliper and generating reading displayed on the LCD.

In touch sensing, the user’s finger serves as the second plate of a capacitor that is connected to an interface circuit. The change in capacitance that happens when the finger hits the second plate is sensed by the circuit, which subsequently generates a trigger signal, imitating the function of a classic electromechanical pushbutton. Another conductive surface can be used instead of a finger, and this is the foundation for the caliper’s implementation.

All of this occurs as a result of analog interface circuitry comprising a timer (oscillator) whose frequency is determined by a resistor/capacitor (RC) time constant, and capacitance variations change that frequency. A frequency-to-voltage converter measures these minute variations in capacitance; the resulting voltage is proportional to the caliper’s location. The values recorded on the LCD display may thus be readily converted into metric, imperial, or fractional units, and the readings can be easily reset to zero again by pressing the zero button, making calibration considerably easier than with conventional calipers.

As a result, the digital caliper is not only an upgraded and improved version of the analogue vernier caliper, but it is also more accurate, reliable, and requires less maintenance. Depending on the nature of the use, they are built of stainless steel or steel. Although both the devices are meant to perform the same tasks however are very different from each other in terms of slight parts and features and not specifically their applications.


How a caliper works is different from each other. The vernier calipers work by sliding and using a vernier scale to provide the reading. The dial calipers work through its rack and pinion system. They move the dial and show the reading. The last one is the digital caliper which works by the electronic system embedded inside the caliper that engineers the electrical charge into numbers.

From the three direct calipers above, we know that vernier caliper is the easiest one to understand while the rest of the calipers have the system works behind the scene.

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