Even though the majority of new calipers are digital, a purely mechanical Vernier caliper still has it's place in the workshop.

Unlike digital or dial counterparts a Vernier caliper:

  • will stay accurate and precise for decades,
  • isn't affected by temperature,
  • works underwater,
  • doesn't require batteries,
  • can be frozen, boiled, buried, burnt or greased and it will still work,
  • isn't affected by strong magnetic field and
  • dropping it will likely not damage it in any way.

This caliper given to me by my father-in-law is a case in point. He worked as a construction engineer, but has been retired for 20 years now. He used this caliper when he was still employed, so I wouldn't be surprised if it's much older than me and I'm in my mid 30's. However, it still works without fail as the day it left the factory (which itself is probably long gone). These things simply last forever.

Despite their daunting look, a Vernier caliper is easy to use and allows for high accuracy, high precision measurements.

You can measure three different dimensions; external using the larger jaws, internal using the smaller jaws and depth using the probe at the end. You'll read the measurements for all three in exactly the same way.

Measuring external dimensions.
Measuring internal dimensions.
Measuring depth.

The main scale is used to read millimetres and the Vernier scale is used for micrometres.

The numbers on the main scale represent centimetres (also inches on the upper part). Each mark on the main scale is 1 millimetre. The numbers on the Vernier scale represent micrometres. Each mark is 20 micrometres (or 0,02 millimetres).

How to measure

Gently close the jaws around the object that you're trying to measure. Since we're looking for sub-millimetre results, pressing too hard against the object can negatively affect the measurement.

Next, find the position of the 0 on the Vernier scale and notice where it falls on the main scale. Do not look at the edge, but only at the 0 mark! This will give you the millimetre part of your measurement.

Vernier 0 is between 5mm and 6mm on the main scale.

In the photo above, the 0 falls between 5mm and 6mm so the final result will be within this range. You can already estimate if it's closer to 5mm or 6mm by whichever is closer to the 0.

In this case, the Vernier 0 is closer to 5, so we can estimate the final result with be around 5,2mm.
Here, the Vernier 0 is closer to 6mm, so we can estimate a final result of around 5,8mm.

Finally, find the tick mark on the Vernier scale that best aligns with one of the markings on the main scale. You already have an estimated guess from the main scale. In the photo below, the Vernier 0 is closer to 5mm on the main scale, so look at the left half on the Vernier scale. Each mark between the numbers on the Vernier scale represents 0,02mm. This will give you the micrometres part of the result.

Main and Vernier marks align best at this point. Because each mark on the Vernier scale is 0,02 and the highlighted mark is 4 spaces to the right of 2 (or, alternatively, 1 space left of 3), we read it as ,28mm.

To get the final measurement, simply combine the two numbers together, separated by a decimal point.

Calipers of lesser quality will have a so called zero error. If you close the jaws completely, the 0 marks on main and Vernier scales should align perfectly.

A high quality caliper, like this one, has no zero error.

If they don't, calculate the value as you did before (but with the jaws completely closed) and write it down somewhere. Then, subtract that value from each of your future measurements to compensate for the zero error.

More examples

We read 6 at the end because the marks align at 3 spaces right of the 7 on the Vernier scale. It is just a coincidence that they also align with the 6 on the main scale!
If the marks align at the last 0 on the Vernier scale, then the micrometres part is exactly 0.

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