Vernier calipers are versatile measuring instruments. It will accurately measure depth, outside dimensions (O.D.) and inside dimensions (I.D.).  

There are 3 main types of calipers: Vernier Caliper, Digital Caliper, and Dial caliper. The designs are very similar, differing only by the way the measurement is displayed.

Most easily understood is the digital caliper, using the jaws to take a measurement that will be displayed on a screen. The down side of the digital is the need for batteries to operate and the higher cost, although they are becoming more accessible.

Dial calipers are also very easy to read, using a needle that moves around a scale to a measurement position on a dial. The down side to dial calipers is usually cost.

The vernier calipers uses a vernier scale to display the measurement and is the simplest design of the three.

Anatomy

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Outside jaws: used to measure external diameter or width of an object  

Inside jaws: used to measure internal diameter of an object

Depth probe: used to measure depths of an object or a hole

Main scale: scale marked every mm or inches and fractions

Vernier scale gives interpolated measurements

Retainer: used to block movable part to allow the easy transferring of a measurement

Screw: used to lock the jaws

Here are some examples of how vernier calipers are used. Part of its versatility is that it can measure a variety of shapes accurately.

Imperial Scale

When using a vernier scale you should check to see what kind of measurement the caliper is calibrated for. This model is in fractional increments instead of decimal, so our reference point is where the 0 on the imperial vernier scale lines up on the main scale (Triangle A). It is two hash marks past the the 1” mark, 2 hash marks would be 2/16 or 1/8 of an inch.  That puts our first number at 1 1/8” now we want to know how much further the mark A is from the 1 1/8" and then we will add these two numbers together to get the proper measurement. So go along the vernier scale and find the only mark that lines up perfectly with any hash mark on the main scale (Triangle B). In this case it is the 4. Now looking at the table on the right side of the scale (Triangle C) we see that it’s graduations are in 1/128” so we will add 4/128 or 1/32 of an inch to our 1 1/8”. To do the math properly we need to get our common denominator so 1 1/8" becomes 1 4/32". Next we add 1 4/32 (Triangle A )+1/32 (Triangle B)=1 5/32.” So the final measurement is 1 5/32."

Metric Scale

The reference point for the metric scale is located at the 0 on the metric vernier scale (Arrow A).

It is beyond the 2.9cm mark. So 2.9cm is our first number and now we want to know how far past the 2.9cm mark we are. Now look at the hash marks on the metric vernier scale and find the only mark that lines up perfectly with any hash mark on the main scale (Arrow B). In this case it is the 4, again and according to the table on the right side of the metric vernier scale we know that each hash mark is worth .05mm, so our second measurement is 0.2mm or 0.02cm. Add these two numbers together and the total measurement is 2.92cm.