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Each centimetre is divided into 10 millimetres. So, 1 mm is 0.1 cm, 2 mm is 0.2 cm, and so on.
2.4 cm will mean 2 cm and 4 mm.

Let us measure a line segment, say AB, using a ruler.
A B

We place the ruler along the line
segment AB , such that the zero mark
of the ruler coincides with point A.
We read the mark on the ruler that
coincides with point B. It lies along
the second division after the 6 cm
marking.
Hence, the length of AB is 6 cm
2 mm, or 6.2 cm.
However, there is a chance for errors in this procedure. The thickness of the ruler may cause
difficulties in reading it. Errors can also happen due to angular viewing.
Hence, for correct measurement, the eye should be positioned just vertically above the mark.

We can avoid such errors by using a divider.
To get the accurate length of line segment AB using a divider and ruler, we open the divider and
place the tips of its arms on the end points A and B of the line segment.
Now, we place the divider without disturbing its opening on the ruler,
so that the tip of its one arm coincides with the zero mark.

A B

Then, we read the mark against the tip of other arm of the divider.
This is the length of line segment AB. Clearly, the length of AB = 4.4 cm.

Example 5: If A, B, and C are three points on a line
such that AB = 5 cm, BC = 3 cm and AC = 8 cm, which Quick Check
one of them lies between the other two?
Solution: We have AB + BC = 5 cm + 3 cm = 8 cm = AC Draw any line segment, say PQ . Take any
point R lying in between P and Q. Measure the
5 cm 3 cm
A B C lengths of PQ , PR and QR .
It means B lies between A and C. Is PQ = PR + QR ?

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