5. Face Right If the vertical circle of the instrument is on the right side of the observer while taking a reading ,the position is called the face right and the observation taken on the horizontal or vertical circle in this position, is known as the face right observation. 6. Changing Face It is the operation of bringing the vertical circle to the right of the observer ,if originally it is to the left , and vice – versa. It is done in two steps; Firstly revolve the telescope through 1800 in a vertical plane and then rotate it through 1800 in the horizontal plane i.e first transit the telescope and then swing it through 1800. 7. Line of Collimation It is also known as the line of sight .It is an imaginary line joining the intersection of the cross- hairs of the diaphragm to the optical centre of the object- glass and its continuation. 8.Axis of the telescope It is also known an imaginary line joining the optical centre of the object- glass to the centre of eye piece. 9. Axis of the Level Tube It is also called the bubble line. It is a straight line tangential to the longitudinal curve of the level tube at the centre of the tube. It is horizontal when the bubble is in the centre. 10 . Axis of the Level Tube It is also called the bubble line It is a straight line tangential to the longitudinal curve of the level tube at the centre of the tube. It is horizontal when the bubble is in the centre. 11. Vertical Axis It is the axis about which the telescope can be rotated in the horizontal plane. ADJUSTMENT OF A THEODOLITE Permanent adjustments: The permanent adjustments in case of a transit theodolites are :- 1.Adjustment of Horizontal Plate Levels. The axis of the plate levels must be perpendicular to the vertical axis. 2.Collimation Adjustment. The line of collimation should coincide with the axis of the telescope and the axis of the objective slide and should be at right angles to the horizontal axis. 3.Horizontal axis adjustment. The horizontal axis must be perpendicular to the vertical axis.
5. Face Right If the vertical circle of the instrument is on the right side of the observer while taking a reading ,the position is called the face right and the observation taken on the horizontal or vertical circle in this position, is known as the face right observation. 6. Changing Face It is the operation of bringing the vertical circle to the right of the observer ,if originally it is to the left , and vice – versa. It is done in two steps; Firstly revolve the telescope through 1800 in a vertical plane and then rotate it through 1800 in the horizontal plane i.e first transit the telescope and then swing it through 1800. 7. Line of Collimation It is also known as the line of sight .It is an imaginary line joining the intersection of the cross- hairs of the diaphragm to the optical centre of the object- glass and its continuation. 8.Axis of the telescope It is also known an imaginary line joining the optical centre of the object- glass to the centre of eye piece. 9. Axis of the Level Tube It is also called the bubble line. It is a straight line tangential to the longitudinal curve of the level tube at the centre of the tube. It is horizontal when the bubble is in the centre. 10 . Axis of the Level Tube It is also called the bubble line It is a straight line tangential to the longitudinal curve of the level tube at the centre of the tube. It is horizontal when the bubble is in the centre. 11. Vertical Axis It is the axis about which the telescope can be rotated in the horizontal plane. ADJUSTMENT OF A THEODOLITE Permanent adjustments: The permanent adjustments in case of a transit theodolites are :- 1.Adjustment of Horizontal Plate Levels. The axis of the plate levels must be perpendicular to the vertical axis. 2.Collimation Adjustment. The line of collimation should coincide with the axis of the telescope and the axis of the objective slide and should be at right angles to the horizontal axis. 3.Horizontal axis adjustment. The horizontal axis must be perpendicular to the vertical axis.
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