Explanation

• Height of Instrument (H.I.) is the elevation of the line of sight when the surveying instrument is correctly leveled.
• Formula:
• H.I.=Elevation of B.M.+B.S.​

Explanation

• Back sight: The first reading taken after setup, always on a point of known elevation.

Additional information 

• Fore sight: The last reading taken before moving the instrument.
• Intermediate sight: Any reading taken between the back sight and fore sight.
• Reduced level: A calculated ground height, not an instrument reading.

Explanation

• Ridge Line: Best for hilly terrain because it sits on high ground.
• Natural water flows away from the road, minimizing the need for costly bridges and culverts.

Additional information:

• Valley Line: Avoided due to flood risks and the need for frequent stream crossings.
• Contour Line: Used mainly for irrigation canals, not highways.
• Drainage Line: Avoided completely due to water erosion

Explanation

• Brass (Handles): Used for handles because it is corrosion-resistant.
• Handles feature a swivel joint to prevent the chain from twisting

Additional information

• Steel (Links): Used for the links and rings, not the handles
• Measurement: The total chain length is measured from the outside edge of one brass handle to the outside edge of the other.

Explanation

• A 20 m metric chain has 100 links.
• Therefore, the length of each link is 20 cm.
• Each link is connected by small rings.
• Metric chains are commonly used in land surveying.