Length and its measurement
As we have studied in the last section, length is the distance between two points and it is measured in terms of metres. Different types of devices are used to measure lengths. For example to measure the length of your table, you will use a ruler or measuring tape. But to measure the diameter (thickness) of a wire, you will require a screw gauge. These devices had been made by comparing them with a standard length called standard metre. The standard metre is a fixed length decided by scientists and accepted by all.

Using a scale to measure length
To measure the length of a given line segment AB (Fig 1.3), the metre scale is kept along the line segment with its graduations parallel to it. The metre scale must be so placed that its divisions are as close as possible to the line segment to be measured. Its zero end is made coincident with one end of the line segment. Note the point where the other end of the line segment lies. Suppose, it lies beyond the 2 cm mark and is coincident with the second small division after it. Since each of these marks is 1 mm, the total length of the line segment is
2 cm + 2 mm = 2 cm + 0.2 cm = 2.2 cm