The diagram below shows a stick placed along a metre ruler. The length of the stick is measured keeping the eye at positions A, B and C.

(a) Write the length of stick PQ as observed, for each position of the eye. Are they all same ?

(b) Which is the correct position of the eye? Write the correct length of the stick.

(a) For A position :

PQ = 3.4 cm

For B position :

PQ = 3.2 cm

For A position :

PQ = 3.0 cm

No, length of PQ observed from positions A, B and C are not same.

(b) The correct position for the eye is position B due to low parallax error. The correct length of PQ is 3.2 cm.