Using a Divider to Measure Length
A divider is used to measure the distance between two points. The correct use of a divider can give a fairly accurate measurement. The divider is placed  such that its two points are at the two ends of the length to be measured. Then, without disturbing the divider, the distance between the two points is measured with  a ruler .

Measuring the Length of a curved Line
We can measure the length of a curved line by using a string. The string is placed along the curved line and its ends are marked on the string The length of the string between the marked points is measured with a ruler .