i) One end of the object to be measured has to coincide with 'O' of the scale.
ii) Measure the quantities using suitable measuring units and express them with suitable multiple and submultiples.
iii) Always keep the object parallel to the scale. 
iv) Our eye must be exactly in front of vertically above the point where the measurement has to be taken.

We know, 1km = 1000 m.
\(\therefore\)  43.65 km = 43.65 x 1000 m = 43650 m
1m = 100cm 
43650m = 100 x 43650
= 43,65,000 cm
43.65 km = 43,650 m
= 43,65,000 cm.

Mass is the measure of the amount of matter in an object.

The comparison of an unknown quantity with some known quantity is known as measurement.

The volume of irregular objects can be measured by the water displacement method.

The length of the pencil = Difference of two readings
= 12.1- 2.0 cm
= 10.1 cm
Length of the pencil = 10.1cm.

1000 m = 1km
\(2250 \mathrm{~m}=\frac{1}{1000} \times 2250\) 
= 2.250 km

Measuring the volume of irregular solid by displacement method.

(i) Take a graduated measuring cylinder and a stone.
(ii) Fill with water to certain level and mark it.
(iii) Tie the stone with a piece of fine thread.
(iv) Immerse the stone completely in to the water.
(v) We can observe the water level and mark it.
(vi) The water level is increased.
(vii) Find the increased level of water.
(vii) It would be equal to the space taken by stone.
(viii) This will be the volume of irregular stone.

Method 1:
(i) Place a string along the curved line, Make sure that the stringcovers every bit of the curved line.
(ii) Mark the points where the curved line begins and ends on the string.
(iii) Now, stretch the string along the length of a meter scale and measure the distance between the two markings of the string.
(iv) This will give us the length of a curved line.
Method 2:
(i) Draw a curved line AB on a piece of paper.
(ii) Separate the legs of the divider by 0.5 cm or 1 cm using a ruler.
(iii) Place it on the curved line starting from one end. Mark the position of the other end. Move it along the line again and again cutting the line into number of segments of equal lengths. The remaining parts of the line can be measured using a scale.
(iv) Count the number of segments.
(v) Therefore, the length of the line = (number of segments x length of each segment) + length of the left over part.

1 millimetre < 1 centimetre < 1 Metre < 1 kilometre.