The true meridians at different places are parallel to each other.

The true meridian at any place is not variable.

The true meridians converge to a point in northern and southern hemispheres.

The maps prepared by national survey departments of any country are based on true meridians.

0° 30'

89° 30'

90° 30'

269° 30'

the magnetic needle moves with the box

the line of the sight does not move with the box

the magnetic needle and graduated circle do not move with the box

the graduated circle is fixed to the box and the magnetic needle always remains in the N-S direction

the forebearing of AB and back bearing of AB differ by 180°

the forebearing of AB and back bearing of BA differ by 180°

both (a) and (b) are correct.

none is correct

incorrect levelling of the magnetic needle

loss of magnetism of the needle

friction of the needle at the pivot

presence of magnetic substances near the instrument