How to Read A Caliper

Measurement with Digital Caliper
How to Read A Caliper

There are three classifications based on how to read the caliper: 1) Vernier caliper, 2) Dial caliper, and 3) Digital caliper. The first one uses a vernier scale, while the second one uses a dial gauge, while the third one uses electronic components. Each of them looks different and has a different working mechanism.

Reading a caliper is not rocket science, but not as easy as reading a ruler. There is a little bit you need to know first. Some of them, vernier and dial caliper, have the main and the second scale. You will add those two reading to get the measurement result. On the other hand, a digital caliper needs no adding. You just read the reading on the LCD screen.

How to Read A Vernier Caliper

A vernier caliper is the most time-consuming caliper. You will potentially experience a human error while using it. Therefore, you need to be familiar to use it. However, it’s the most durable caliper. In this practice, as an example, we are going to measure the outside diameter of a nail body.

1. Quantifying the Main Scale

The first step of the measurement starts from the main scale. From the video above, the main scale provides graduations in metric (mm) and imperial (inch). The smallest division of the metric represents 1mm and the imperial represents 1/16 of an inch.

Reading A Vernier Caliper
The part that lines up (This picture is taken from the video above)

To read the reading on the main scale, quantify how many divisions that are passed by the mark O of the vernier scale over the main scale. On the picture, we can easily see there are 3 divisions on the metric vernier scale and 2 divisions on the imperial vernier scale. So, the main scale displays 3 x 1mm = 3mm (metric) or 2 x 1/16 = 1/8inch (imperial).

2. Quantifying the Vernier Scale

The second step is the vernier scale. The same with the main scale, it provides graduations in metric and imperial. One division of the metric scale will be multiplied by 0.05mm. And one division of vernier scale will be multiplied by 1/128 of an inch.

Need to know that there are actually 10 divisions on the metric vernier. The shorter line divides into two half of a division (0.5 division). On the other hand, there are 8 divisions on the imperial vernier. Need to remember, it is a rule when no one that lines up except the 0 and 8, it will be multiplied by 0.

Count how many divisions from 0 to the two lines of both main and vernier scale that line up. In this case, the red line shows it is. The result is 1.5 divisions on the metric vernier and 8 divisions on the imperial vernier. So, 1.5 x 0.05mm = 0.075 mm (metric) or 0inch (imperial). Remember that the line that lines up on the imperial vernier scale is 0 and 8, it’s multiplied by 0.

3. Calculating the Result

Reading the Vernier Caliper in mm

Main Scale + Vernier Scale = Result

( 3 x 1mm ) + ( 1.5 x 0.05mm ) = 3 mm + 0.075 mm = 3.075 mm

Reading the Vernier Caliper in inch

Main Scale + Vernier Scale = Result

( 2 x 1/16inch ) + ( 8 x 0 ) = 1/8 inch + 0 = 1/8 inch

Reading A Vernier Caliper with Zero Error

No Zero Error
No Zero Error

If there is zero error then the measurement is not accurate. To check it, close the jaws carefully and find out whether the mark 0 of both scales (vernier and main scale) line up. If they are not aligned up, there is zero error. When the mark 0 of the vernier scale is on the left of mark 0 of the main scale, then the zero error is negative, it is positive otherwise. However, in most cases, positive is common to happen.

In this case, we are not trying to fix the zero error. It takes time to fix it. Therefore, we are going to make some adding or subtracting based on the value of the zero error.

Suppose the mark 0 of vernier scale is 1 mm to the right of mark 0 of the main scale. You need to subtract this value from the original reading: 3.075 mm – ( 1 mm ) = 2.075 mm. Conversely, if it is to the left which means negative 1mm, then you will subtract this negative number from the original reading: 3.075 mm – ( – 1 mm ) = 4.075 mm.

How to Read A Dial Caliper

Reading a dial caliper is quite similar to the vernier caliper. However, the dial caliper consists of a dial meter instead of a vernier scale. The components of the dial caliper are the main scale and the dial. The readings are taken from these two pieces.

In the dial caliper showed on the video below, it has 0.1mm resolution and metric graduated only. The smallest division of the main scale is 1mm while the smallest scale of the vernier meter is 0.1mm. Each one rotation on the dial gauge represents 1cm on the main scale.

1. Reading the Main Scale

Take a look where the pointer of the main scale resides. The reading result of the main scale is the closest mark that has been passed by the pointer. On the video above, we know it’s 0cm.

2. Reading the Dial

Count how many divisions the pointer points. Easily we know it is 31 divisions. Simply, 31 x 0.1mm = 3.1mm.

3. Final Measurement

The final measurement is taken by combing the two readings of the main scale and the dial. In mathematical form: 0 cm + 3.1mm = 3.1mm.

How to Read A Digital Caliper

A digital caliper is the caliper advanced version. It requires less time and effort to take measurements. The most contrast part of a digital caliper is the digital display along with some buttons on it. Instead of taking hours to note down the readings, you can take the measurements within minutes.

To know the measurement result, simply read out the reading on the LCD without doing any adding or substracting. On the video above, we can see that the outside diameter of the nail is 3.1mm. It’s quick, easy, and accurate.

Most digital calipers have a conversion button that allows the users to convert the reading from mm to inch or vice versa.

Reading A Digital Caliper with Zero Error

Need to know that the first step you need to take care when reading a digital caliper is that the scale has to display zero reading (showing number 0) when all the jaws are closed. If you mistakenly miss this step then there is a chance that your reading is not accurate.

When you close the jaws but the reading shows a particular number, then it indicates zero error. Solving this issue is tremendously easy. Unlike a vernier caliper, it’s digital and there is no way to calibrate it in a manual way. Therefore, a digital caliper is equipped with a zero button. Just push the button “zero” or the related one when you close the jaws. It will turn back the number to 0. Make sure the jaws are truly closed before pushing the zero button.

After you are sure that the zero error has been faded out, you can continue to make a measurement.

A Little Closing On How to Read A Caliper

From the three types above, which type of caliper is the easiest one to read? Surely, you can answer quickly it’s digital caliper. The second rank is dial caliper. And the last rank is vernier caliper.

Reading vernier caliper needs good eyesight to identify which mark both on the main scale and the second scale that encounter. This is important because it affects accuracy. Similarly, reading a dial caliper needs a good vision as well. A wrong angle when reading it affects too. The most automatic one is digital, once the object is secured, the number immediately appears on the LCD.

In order to get the right measurements, make sure the jaws of the digital calipers are clean. Moreover, the zero error must be checked first before taking the reading.