MEASUREMENT OF LENGTH 
The length of an object is the distance between its ends.  It can be measured using a ruler, a measuring tape, a metre rod , and so on  whichever is convenient for the required purpose.

A ruler

While measuring length using a ruler, we have to take the following precautions :
(i)     Care should be taken to keep the ruler along the length of the object.

The ruler should be kept along the length of the object.

(ii) If the edge of the ruler is worn out or broken, the measurement should be stared from any  other mark that is fully clear. 

Measurement should only be started from a mark that is fully clear.

(iii)  Eyes should be exactly above of the point  where the measurement is to be taken.

Some measurements

 Non-standard measures:  The lengths of steps, arms, hands, or fingers of different people are different, therefore the distance measured with their help is not always     reliable. These methods are, therefore, called non-standard measures.

 The lengths of steps, arms, hands, or fingers of different people are different, therefore the distance measured with their help is not always reliable.

 These methods are, therefore, called non-standard measures. While measuring things, accuracy is needed.

  A variety of units can be used for this purpose.