Fundamentals of Surveying (FS) Practice Exam

In leveling, what does the term "height of instrument" refer to?

1. The distance from the ground to the axis of the telescope

2. The elevation of the line of sight above the datum being used

3. The height of the line of sight above a benchmark

4. All of the above

The correct answer is: The elevation of the line of sight above the datum being used

The term "height of instrument" refers to the elevation of the line of sight above the datum being used. This concept is crucial in leveling because it determines the point from which measurements are taken and how accurate those measurements will be. In leveling, the height of instrument is calculated by taking the height from where the instrument is set up, often called the instrument's station. This height is vital for ensuring that the level’s readings are accurate, as it helps establish a reference point for measuring vertical distances to other points on the ground. By knowing the height of the instrument above the datum, surveyors can make precise calculations of elevation differences between points. The other choices incorporate related concepts but do not fully capture the essence of what "height of instrument" specifically refers to in leveling practices. While the distance from the ground to the axis of the telescope does contribute to the overall understanding of the instrument setup, it is not what is meant by the term. Similarly, the height of the line of sight above a benchmark is indeed important, but the focus of the term is on the elevation relative to the chosen datum for leveling purposes. Therefore, the most accurate definition aligns with the concept of the height of the line of sight above the selected datum.