# The line passing through the intersection of the horizontal and vertical cross hairs and optical centre of the subject glass and its continuation is c

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The line passing through the intersection of the horizontal and vertical cross hairs and optical centre of the subject glass and its continuation is called:
1. the line of sight
2. the line of collimation
3. the line of sight as well as the line of collimation
4. the axis of level tube
5. the centre line

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Correct Answer - Option 3 : the line of sight as well as the line of collimation

Explanation

1.Line of sight: It is the imaginary line passing through the intersection of the crosshair on the diaphragm and the optical center of the objective lens.

when a line of sight comes in a horizontal plane, it is called a line of collimation.

The line of sight generates a vertical plane when the horizontal axis is perpendicular to the vertical axis.

2. Line of collimation: It is an imaginary line passing through the intersection of the crosshairs at the diaphragm and the optical center of the object-glass and its continuation.

3. Axis of Bubble tube: It is an imaginary line tangential to the longitudinal curve of the bubble tube at its midpoint.

4. Axis of a telescope: This axis is an imaginary passing through the optical center of the object-glass and the optical center of the eye-piece.