What are Vernier Calipers?
There are several types of calipers out in the world, and one of the handiest is the vernier caliper. This common tool is simple yet precise. It has a jaw-like structure at the end of a ruler. Securing the jaw on either side of the measured item provides stable and accurate measurement.
Although they are simple, Vernier calipers have a lot of precision to their design, resulting in reliably accurate reads. They can be used for numerous things, but none of their purposes are possible without their unique design. Knowing what makes a Vernier different from other calipers will help you make the most of this measuring device.
What is the Vernier scale?
The Vernier caliper is named for a scale, which dates to 1631. A French mathematician named Pierre Vernier saw a need for more precise measurements. Vernier took it upon himself to develop a new type of measuring scale. His Vernier scale added a second, smaller scale than the measurement scale that was already there. By using the smaller scale as a secondary measurement within the larger, one could obtain finer precision.
Initially, Monsieur Vernier created this scale to be used in instruments that would measure angles. However, the scale is most often used in calipers. Its extra layer of precision gives the accuracy that many industries require when measuring an object’s dimensions.
As with the caliper design itself, the Vernier scale is simple yet ingenious. It delivers an accurate read by relying on the human ability to detect the alignment of lines. Our eyes are much better at noticing whether two lines are misaligned or aligned than they are at reading tiny, close measurements. With the Vernier scale, we need only to find the lines that match to know the precise measurement.
The Vernier scale is what sets the Vernier caliper apart from other measurement tools. While a standard ruler may only be able to read measurements up to one-tenth of an inch, a Vernier caliper can measure as precisely as 0.001 inches. This difference is huge when it comes to working in fields like mechanical engineering or metalworking.
How to read a Vernier caliper
Each Vernier caliper has two scales. There is a main scale and a Vernier scale. The main scale is located on the length of the ruler, along which the jaws slide open and closed. You’ll find the Vernier scale on the bottom jaw. This allows the Vernier scale to move along the main scale during measurement. That movement is key in reading the Vernier scale.
The main scale will either measure by the millimeter or the tenth of an inch. For the sake of explanation, we’ll assume that we’re working with a metric caliper rather than an imperial one.
Each mark on the main metric scale represents one millimeter. The main marks on the Vernier scale, which are numbered zero to ten, represent one-tenth of a millimeter.
To read the main scale, look at the zero mark on the Vernier scale, not the edge of the jaw. The zero mark on the Vernier scale will indicate the measurement on the main scale.
This significant detail is evident if you close a Vernier caliper. Let the jaws come together so that the measurement is zero, and you will see that the Vernier zero lines up with the zero on the main scale. This indicates that the measurement is zero. If you measure something that you know is, for example, seven millimeters, then the Vernier scale zero will line up perfectly with the seven-millimeter mark.
But what if the Vernier scale zero doesn’t line up perfectly? That’s where the brilliance of the Vernier scale comes into play.
Let’s say that the Vernier scale zero falls roughly halfway between the six-millimeter mark and the seven-millimeter mark. You could use the naked human eye and assume that it’s six and a half millimeters. But, with that method, there is too much room for error.
To get the accuracy that we need, we will look at the rest of the Vernier scale. Search along the Vernier scale markings to find the line that is most accurately aligned with one of the markings on the main scale. Since the zero-marking seemed to fall halfway between the two main scale markings, we can infer that it will be a number closer to five. Once we look at the Vernier scale, we’ll see that the six-mark lines up best with a mark on the main scale. This means that it’s six-tenths of a millimeter. Therefore, our reading would be 6.6 millimeters.
When you’re reading a Vernier caliper with smaller measurement options, you’ll see additional markings on the Vernier scale. These may measure something like .02 millimeters. Its exact measurement will be marked on the caliper. You should also look at these markings when you’re reading a measurement. You may find that one of the smaller lines matches the best with the main scale, and could get an even more precise read, like 6.62 or 6.64 millimeters.
When to use a Vernier caliper
Metalworking, woodworking, mechanical engineering, forestry — these industries and more have a place for the Vernier caliper. Any trade that requires precision should use a Vernier caliper for obtaining dimensional measurements.
There are multiple ways to put the Vernier caliper to use, and even more purposes that call for its services. The large jaws can clamp on the exterior of an object. It’s often used this way in industries like the steel sector when it’s necessary to measure the outer breadth of a rod.
Smaller jaws are built into the caliper as well. These are located above the main jaws, so that they move along the same Vernier scale. The smaller jaws, also known as internal jaws, are designed to measure the internal breadth of an object.
Vernier calipers are also built with a depth measuring rod at the end of the main scale. The rod protrudes as you turn the thumbscrew and provides accurate reads on holes and other depths.
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Phil Wiseman is Chief Marketing Officer at Alliance Calibration. He earned a B.S. in Chemical Physics from Centre College. Phil is an ASQ Certified Quality Auditor and ASQ Certified Manager of Quality/Organizational Excellence.