Length is defined as the distance between two points. The SI unit of length is metre.

Upper jaws.

Full form of SI system is "International system of units"

A standard unit is defined as a specific magnitude of a physical quantity that has been adopted by law or convention.

Measurement is defined as the determination of the size or magnitude of something.

Mass m = 5 kg
Acceleration due to gravity g = 9.8 ms^-1
Weight W = m x g = 5 x 9.8 = 49 N
Therefore the weight of an object is 49 N

i) Standard units give the correct and accurate measurement like length, mass, time etc...
ii) It is not varied from person to person, place to place and object to object. So we need standard unit.

1. The units named after scientists are not written with a capital intial letter.
Ex: newton, henry, ampere and watt
2. The symbols of units named after scientists should be written by the initial capital letter.
Ex: N for newton, H for henry, A for ampere and W for watt.
3. Small letters are used as symbols for units not derived from a proper noun.
Ex: m for metre, kg for kilogram
4. No full stop or other punctuation marks should be used within or at the end of the symbols.
Ex: 50 m and not as 50 m.
5. The symbols of the units are not expressed in plural form.
Ex: 10 kg not as 10 kgs.
6. Accepted symbols should only be used.
Ex: ampere should not be written as amp and second should not be written as sec.

(i) Determine the pitch, the least count and the zero error of the screw gauge.
(ii) Place the wire between the two slides.
(iii) Rotate the head until the wire is held firmly but not tightly with the help of ratchet.
(iv) Note the P.S.R and H.S.R
(v) The diameter of the wire is given by
     P.S.R + (H.S.C x L.C) ± Z.C,
(vi) Repeat the experiment for different portions of the wire.
(vii) Tabulate the readings.
(viii) The average of the last column reading gives the diameter of the wire.

(ix) The average gives the correct reading.

(i) The first step in using the Vernier caliper is to find out its least count, range and zero error.
(ii) \(Least\ count\ of\ the\ instrument(LC)=\frac{Value\ of\ one\ smallest\ main\ scale\ division}{Total\ number\ of\ vernier\ scale\ division}\)
The main scale division can easily be obtained by inspecting the main scale. It will be in centimeter, further divided into millimetre. The value of the smallest, main scale division is 1 mm. The Vernier scale division is obtained by counting number of division in it. In the Vernier scale there will be 10 divisions.
\(LC=\frac{1mm}{10}=0.1\ mm\)
(iii) Unscrew the slider and move it to the left, such that both the jaws touch each other.
(iv) If they are not coinciding with each other, the instrument is said to posses zero error. Zero error may be positive or negative. If the zero mark of the Vernier is shifted to the right, it is called negative error. On the other hand, if the Vernier zero is shifted to the left of the main scale zero marking, then the error is positive.
(v) Once you are able to calculate the zero error, you can get the correct reading using the formula:
The correct reading = Main scale reading + (VC x LC) - (Zero correction)
(vi) We can use Vernier caliper to find different dimensions of any familiar object.

The thickness of coin (one rupee) is finding with the help of screw gauge:
1. Determine the pitch, least count and the zero error of the screw gauge.
2. Place the coin between two studs.
3. Rotate the head until the coin is held firmly but no tightly with the help of the ratchat.
4. Note the reading of a pitch scale crossed by the head scale and the head scale (PSR) division that coincides with the pitch scale axis (HSC).
5. The thickness of the coin is given by PSR + (HSR + ZC) x LC. Repeat the experiment for the different position of the coin.
6. Tabulate the reading.
7. The average of the reading given the thickness of the coin.

The thickness of one rupee coin is = 1.33 mm.