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## 2. Slope Reduction

A surveyor measures the distance between a section and quarter section corners and records a slope distance of 2677.36 ft with a zenith angle of 81°10'25" corrected for atmospheric conditions.

What error is introduced in the horizontal distance if refraction and curvature are not taken into account?

To solve this, compute the difference using Equations (A-2) and (B-5)

From Equation (A-2)

From Equation (B-5)

The difference is 0.096 ft for a relative accuracy of 1/27,600.

While this is a pretty good relative accuracy, remember that this is just for an error introduced by ignoring refraction and curvature. It doesn't take into account other errors which can exist in the measurement.