What is the minimum number of NGS first or second order benchmarks used for vertical control?

What is the minimum number of NGS first or second order benchmarks used for vertical control?

• A. One
• B. Four
• C. Three
• D. Two

Answer: (D)

Vertical control relies on precise reference marks with elevations tied to a standard datum. A single benchmark cannot anchor elevations for other points or provide a way to verify leveling accuracy. Using a pair of high-order benchmarks—commonly first- or second-order marks—gives the necessary independent elevation reference and enables checks for consistency. This setup lets you define the vertical connection and propagate elevations to the project area, with redundancy for error detection. Additional markers can improve reliability for larger networks, but the minimum required is a pair of high-order benchmarks.

Vertical control relies on precise reference marks with elevations tied to a standard datum. A single benchmark cannot anchor elevations for other points or provide a way to verify leveling accuracy. Using a pair of high-order benchmarks—commonly first- or second-order marks—gives the necessary independent elevation reference and enables checks for consistency. This setup lets you define the vertical connection and propagate elevations to the project area, with redundancy for error detection. Additional markers can improve reliability for larger networks, but the minimum required is a pair of high-order benchmarks.