Methods of Levelling
- Barometric Levelling: Based on the change in atmospheric pressure with elevation. Less accurate due to atmospheric fluctuations and suitable for reconnaissance works.
- Trigonometric Levelling: Elevations are determined by measuring vertical angles and horizontal distances, with trigonometric relations applied to calculate elevations.
- Spirit Levelling: The most accurate method, where the difference in elevation is determined by measuring vertical distances with respect to a horizontal line using a spirit level attached to a telescope.
Levelling Instruments and Accessories
- Level: Used to provide a horizontal line of sight. Components include:
- Telescope: For line of sight.
- Level Tube: To check if the line of sight is horizontal.
- Levelling Head: Adjusts the bubble tube to the center.
- Tripod: To support the instrument.