Vernier calipers provide a higher degree of accuracy in measuring lengths than comparable tools with most common metric calipers able to measure values in centimetres up to 2 decimal places i. This is possible due to the vernier scale which is attached to the main scale and provides that extra decimal place in the measured reading. Vernier calipers can be used to measure a variety of dimensions of an object such as internal and external diameters or length and depth. The key is to understand how to read a vernier caliper in the proper way and that is what we are going to discuss in this article.

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Vernier calipers provide a higher degree of accuracy in measuring lengths than comparable tools with most common metric calipers able to measure values in centimetres up to 2 decimal places i.

This is possible due to the vernier scale which is attached to the main scale and provides that extra decimal place in the measured reading. Vernier calipers can be used to measure a variety of dimensions of an object such as internal and external diameters or length and depth.

The key is to understand how to read a vernier caliper in the proper way and that is what we are going to discuss in this article. We will assume that you have taken the necessary steps before measurement and positioned the calipers correctly according to the required dimension which needs to be measured and now the scales of the caliper have moved a certain distance to indicate the measured value.

To read this value the first step is: Obtain Main Scale Reading: The Main scale is obviously named because it is the primary scale of a vernier caliper. It is graduated in millimetres or inches. In case of metric units the smallest value that can be measured by the main scale is 1mm. To find out the main scale reading look at the value on the scale directly on the left of the zero mark of the vernier scale. In the example below the value immediately before the zero mark is 2.

The main scale has given us a number but it is not the exact value of the measurement. In the example we can see that the exact value is slightly greater than 2. This will be determined by the vernier scale reading. The total length of the scale represents 1 mm.

Reading the vernier scale requires a bit of observational skill and since it is the most important step of the process we suggest you do this very carefully.

The method is simple. Just look for the line on the vernier scale which is perfectly aligned with mark on the main scale. This value is the vernier scale reading. For example in the above picture the line corresponding to 3 on the vernier scale aligns perfectly so the vernier scale reading is 0. The final step is to simply add the two values to obtain the final reading. Zero Error Adjustment The Zero error can be checked by closing the jaws of the caliper without any object in between.

When the jaws are in close contact with each other, check the position of the zeros on the main scale and the vernier scale. However if they do occur they can be compensated for easily by just measuring the value of the zero error. To do this you have to close the jaws of the caliper and note the value of the vernier scale which coincides with the main scale just like when reading the vernier scale.

This value should then be either added or subtracted from the total reading. If the vernier zero is to the right of the main scale zero when the jaws are closed then the error is a positive zero error. This means that the final value will be more than the actual value so the zero error needs to be subtracted from the final value. In the picture shown above the value of the zero error can be found by looking at the aligned mark on the vernier scale.

This is the 6th mark so the value is 0. So for a zero error of 0. So the error will need to be added to the final reading. Then do it with a real vernier caliper with objects whose dimensions you already know.

With a little practice reading a vernier caliper will become as easy as reading a normal scale.

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## How to Read a Vernier (caliper)

Main article: Vernier acuity Vernier scales work so well because most people are especially good at detecting which of the lines is aligned and misaligned, and that ability gets better with practice, in fact far exceeding the optical capability of the eye. This ability to detect alignment is called Vernier acuity. In case of vernier calipers it occurs when a zero on main scale does not coincide with a zero on vernier scale. The zero error may be of two types: when the scale is towards numbers greater than zero it is positive; else negative.

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## Vernier scale

Close the jaws lightly on the object to be measured. If you are measuring something with a round cross section, make sure that the axis of the object is perpendicular to the caliper. This is necessary to ensure that you are measuring the full diameter and not merely a chord. Ignore the top scale, which is calibrated in inches.