What is a common cause of parallax error in surveying?

Parallax error commonly occurs during the reading of measurements when the observer's eye is not properly aligned with the line of sight of the measurement scale. When the eye is positioned at an angle rather than directly in line with the point being observed, the reading can appear to be shifted from its true position. This discrepancy can lead to measurement errors, making it crucial for surveyors to maintain proper alignment when taking readings.

In surveying, ensuring that the eye is directly above the measurement mark is essential for accuracy. This alignment helps avoid errors that could arise from visual misinterpretation, which could result not only in incorrect readings but also affect various surveying calculations and outcomes.