This device is a very useful tool. It is also commonly used. Please see the following video that was prepared for you. Next, continue the lessons.

The diagram shows the picture of a Vernier caliper.

**Parts of Vernier caliper**

A – Jaws(for measuring outer dimension),

B – Jaws (for measuring inner dimension),

C – Fixed Jaws,

D – Movable Jaws,

E – Locking Screw,

F – Depth Bar,

G – Retainer,

H – Vernier Scale,

I – Main Scale easily.

This device has a Vernier scale and the Main scale. This equipment is calibrated in mm. One division of the main scale is equal to 1mm. 10mm makes 1cm. 10 small divisions on the vernier scale equal to 9 small divisions of the main scale. We can see it when the zero points of both scales are coincident.

**We will now find the small scale of this device.**

The length of 1 division of the Main scale = 1 mm

The length of 9 division of the Vernier scale = 9 mm

Therefore The length of 1 division of the Vernier scale = (9 mm)/10

The smallest measure of the instrument = The value of 1 division of the Main scale – The value of 1 division of the Vernier scale.

The smallest measure of the instrument = 1 mm – (9 mm)/10

= 1 mm – 0.9 mm

** = 0.1 mm**

In this way, Lets us assume the value of one division on the Main scale is** x**,** **and **y **division of the Vernier scale is equal to **z **divisions of the Main scale. Next, we can find the Smallest measure of the instrument. It is **x(1 – z/y)**.

The length of 1 division of the Main scale = **x**

The length of **y** divisions of the Vernier scale = **xz**

Therefore The length of 1 division of the Vernier scale = (**xz)/y**

Smallest measure = The value of 1 MS – The value of 1 VS

= **x – (xz)/y = x(1 – z/y)**

## Zero error

When the two jaws of the Vernier caliper are in contact, the zero of the main scale and the zero of the Vernier scale should coincide. If both the zeros do not coincide, there will be a positive or negative zero error.

### The state of No Zero Error

When the two jaws are in contact, the zero of the main scale and the zero of the Vernier scale should coincide like the following fig. You can see here both zero lines coincide correctly. This is a No Zero Error State.

## Positive zero error

When the jaws of the vernier caliper are just closed and the reading is a positive reading away from the 0.0mm. If the reading is 0.2mm like the following fig, the zero error is referred to as +0.2 mm. The zero lines of the Main scale is on your right side as shown in the following fig.

VS=Vernier Scale

MS=Main Scale

Now lets we learn how to read the positive zero error. First, you find the Here zero error is positive or negative. In this case, it is positive because the zero lines of the Vernier Scale are on your right side from the zero lines of MS. In this case, we have to find the distance between both zero lines(marked with a red circle). That is the zero error we have to find.

Now we have to find the main scale line and a Verner scaling line both coincided. From that line, we find the distance from the zero lines of MS. Here it is 2mm. Now we count the divisions from coincided lines to zero lines of the Verner Scale(VS). Here it is 2. Next, we multiply it by the value of one division of VS. Here it is 2*(0.9) = 1.8mm.

Zero error = distance between both zero lines

= (The length between zero lines of MS and coincided line) -(The length between zero lines of VS and coincided line )

= 2mm – 1.8mm = **+0.2mm**

**Note**– We count divisions between zero line of VS and coincided line(marked with green circle). Here it is 2. Next, we multiply it by the smallest measure of VS. Here it is 2*(0.1mm) = +0.2mm. Lets we assume the reading is X. Then the actual length is X-Positive Zero error. Actual length = X-0.2mm.

## Negative zero error

When the jaws of the vernier caliper are just closed and the reading is a negative reading away from the 0.0mm. If the reading is -0.2mm like the following fig, the zero error is referred to as -0.2 mm. The zero lines of the Main scale is on your left side as shown in the following fig.

Now lets we learn how to read the negative zero error. First, you find the Here also zero error is positive or negative. In this case, it is negative because the zero lines of the Vernier Scale are on your left side from the zero lines of MS. In this case, we have to find the distance between both zero lines(marked with the red circle). That is the zero error we have to find.

Now we have to find the coincided line that the main scale line and the Verner scaling line both coincided. This is also the same as the above positive zero we have done just before. Ok?.

From that line(marked with green circle), we find the distance from the zero lines of MS. Here it is 7mm. Now we count the divisions from coincided lines to zero lines of the Verner Scale(VS). Here it is 8. Next, we multiply it by the value of one division of VS. Here it is 8*(0.9) = 7.2mm.

Zero error = distance between both zero lines

= (The length between zero line of MS and coincided line) -(The length between zero line of VS and coincided line )

= 7.0mm – 7.2mm = **– 0.2mm**

**Note**– We count divisions between the 10th line of VS and coincided line(marked with green circle). Here it is 2. Next, we multiply it by the smallest measure of VS. Here it is 2*(0.1mm) = -0.2mm. Lets we assume the reading is X. Then the actual length is X+Negative Zero error. Actual length = X+0.2mm.

The smallest error in taking measurements on this device is it’s the smallest measurement or half of the smallest measurement. It is 0.1 mm or 0.05mm.

Place the readings from this instrument in 1 decimal place in mm because its smallest measure is 0.1mm. Remember it is very important.

Lets we continue with next lesson. click NEXT

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