Which bottom cross-section dimension is used for the second order accuracy of survey monuments?

• A. 25 x 25
• B. 40 x 40
• C. 35 x 35
• D. 20 x 20

Answer: (B)

Understanding how the size of the monument’s bottom cross-section affects accuracy helps explain why 40 x 40 cm is used for second-order surveys. The bottom cross-section is the footprint of the marker’s base that sits in the ground. A larger, square base provides a stable, broad bearing area, making the marker less susceptible to movement from soil settlement, frost, or minor tilting over time. This stability is essential for maintaining the precise position needed for second-order accuracy, since any shift in the marker can introduce error into all measurements tied to it. Therefore, the 40 x 40 cm base is specified to meet the stability requirements of second-order surveys. Smaller bases would be more prone to movement and thus less suitable for this accuracy level, while other dimensions may be used for different orders or marker types.