When the bubble of the level tube of a level, remains central
(A) Line of sight is horizontal
(B) Axis of the telescope is horizontal
(C) Line of collimation is horizontal
(D) Geometrical axis of the telescope is horizontal
(A) Line of sight is horizontal
(B) Axis of the telescope is horizontal
(C) Line of collimation is horizontal
(D) Geometrical axis of the telescope is horizontal