In slide wire bridge, why do we prefer to obtain the balance point between 35 cm and 65 cm marks ?

35cm – 65 cm of a meter bridge is the middle part of the meter bridge. If the balance point is kept beyond the 35 and 65 cm of the meter bridge wire or is kept between the middle of the meter bridge wire addition of another unknown resistance may displace the null point beyond the range of the meter bridge.

Secondly, it has been found that if the null point of the meter bridge lies near the centre then the sensitivity of a Whetstone’s bridge (on which’s principle meter bridge works) is improved.