**1 (d) Describe how to measure a variety of lengths with appropriate accuracy using tapes, rules, micrometers and calipers using a vernier as necessary.**

In this part we are going to focus on how to measure different lengths, using the appropriate equipment. First, here are the most commonly used units for length

1

**km**= 1000**m**
1

**m**= 100**cm**
1

**cm**= 10**mm**Back to the topic, the instrument's we need to know about are the following .....

**1) Vernier Caliper**

Vernier caliper is used to measure short lengths i.e. 0 to 15

**cm.**It is accurate to 0.01

**cm**. A pair of vernier calipers consists of a Main Scale and a Vernier Scale as shown in the diagram below. The outside jaws, are used to measure the outer dimensions of an object and the inner jaws for the inner ones. The stem is used to measure the depth.

To measure , gently grip the object with the straight edges of outside or inside jaws.

#### How to take reading

First read the main scale, and note down the reading

**before**the 0 on the

**vernier scale**, as shown in the diagram below. The reading on it is 2.8 cm, as the .8 after the 2 on the main scale is before the 0 on the vernier scale.

For the second place of decimal, look at the vernier scale. Find a marking on the vernier scale that coincides exactly with the a reading on the main scale. In the diagram below, the 6 on the vernier scale coincides exactly with a line on the main scale (it does not matter with which line on the main scale this line coincides). So the second place of the decimal would 6, ie .06.

To get the total reading, add the two readings i-e 2.8+.06. The final reading is 2.86cm or 286mm.

**How to avoid zero error**

Before using vernier caliper you should close it to find whether a zero error exists or not

IF THE SCALES ARE LIKE THIS

**Then there is no zero error**

Else if:

- The zero on the vernier scale is on the right side of the zero (on main scale ) then a positive zero error exists . It should be subtracted from the final reading at the end i.e.
**final reading**-**positive zero error**=**accurate reading**e.g. if the reading is 2.15cm and the error is of 0.02cm (**positive zero error**). Then the reading will be 2.15-0.02=2.13cm.

- The zero on the vernier scale is on the left side of the zero on main scale then a
**negative zero error**exists to get an accurate reading then we will add the error in the final reading i.e**final reading**+**negative zero error**=**accurate reading**e.g. from above values 2.15+0.02=2.17.

**2) Micrometer**

Micrometer is used to measure very short readings i.e. 0 to 2.5

**cm**. it has an accuracy of 0.001

**cm or**.01

**mm**. Micrometer has two scales, main scale (on the sleeve) and the circular scale (on the thimble ). Each division on the main scale represents 1 mm. According to o level's pattern each division on the thimble represents a distance of 0.01mm.

(Diagram above shows some main parts of the micrometer)

#### How to take reading

- Turn the thimble until the object is gripped gently.
- Read the main scale on the sleeve. This reading would be in millimeters. In the diagram below, the reading is 5.5mm
- Then read the line on the circular scale that coincides with the line on the main scale. In the diagram below, the 28th line on the circular scale coincides with the line. So, the reading would be 0.28mm.
- Then add 5.5 with 0.28 and you will obtain your answer in millimeters.

#### How to avoid error

When the zero on the vernier scale i.e. circular scale coincides exactly the horizontal line than no error exist.

Else if the zero is

**above**the horizontal line than a

**negative zero error**exists and can be avoided by measuring the

**error**and adding the

**error**into the

**final reading**.

While if the zero is

**below**the horizontal line than a

**positive zero error**exists and can be avoided by

**subtracting**the

**error**from the

**final reading.**

Note: The micrometer should never be tightened to much as it can damage it. it may also introduce errors so aviod over tightening the ratchet. a 'tic' sound is heard when micrometer has been tightened.

####
**General formulas for errors (for vernier caliper and** **micrometer**)

Accurate reading = Final reading plus Negative zero error **General formulas for errors (for vernier caliper and**

**micrometer**)

Accurate reading = Final reading minus Positive zero error.

**3&4) Meter rule and Measuring Tape**

- A meter rule is used to measure medium lengths i.e. 0 to 1m. It has an accuracy of 0.1cm.
- A measuring tape is used to measure long lengths i.e. 0 to 100m . It has an accuracy of 0.1 cm

**always**be taken by keeping your eye perpendicular and directly above the reading.

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ReplyDeletePrecision Machined Components SuppliersGreat post, thank you very much for the info - really helped me! ^.^

ReplyDeleteI'm a British-Pakistani who just moved, and we're doing O Levels, and Physics is quite difficult for me, so this really helped once again!

Verniercalipers Then the user has to note down the value of measurements on the main scale and the Vernier scale. User can use a simple formula and substitute the values of measurement in the formula to get a 100% accurate measurement of the object placed between the jaws of the device.

ReplyDeleteHi, I think your conversion was wrong for the answer, it's 28.6mm, not 286. This was well explained however.

ReplyDeletetell about the pitch as well and u should have labelled the datum line also for better understanding...btw it helped me alot thx

ReplyDeleteThe most common form of error associated with measuring instruments is the parallax error. These errors lie within our control and can be eliminated if the proper measures are taken To read more information about the errors in the measurement visit this link

ReplyDeletehttp://vernierscaliper.com/precautionary-steps-while-taking-measurements-by-vernier-caliper-85.html

In VSR if 0 is conciding with main scale line do we write 0 or we take the cocided line after 0

ReplyDeletePlz...reply soon

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