In vertical deflection, the flat-area deviation is ignored, while mountainous-area deflection values are large and must be considered as systematic error. Which pair completes the sentence?

• A. ignored; large
• B. large; ignored
• C. small; moderate
• D. negligible; negligible

Answer: (A)

In vertical deflection, terrain strongly influences how big the deflection can be. Flat areas have very small deflection values, so these deviations are typically neglected in practice. But in mountainous regions the deflection values become large because the mass of the mountains disturbs the local vertical significantly; these large deflections act as systematic errors that bias measurements and must be accounted for or corrected. So the pair that fits is: ignored; large.