Setting up the Instrument in Undulating Terrain

Undulating terrain refers to a type of terrain that has a series of hills and valleys. When levelling in an undulating terrain, it is important to set up the instrument in the correct location to achieve accurate results.

The correct answer to the question is option B, which means that it is preferable to set up the instrument at the bottom of the valley. This is because:

- Improved accuracy: Setting up the instrument at the bottom of the valley allows for a more accurate measurement of the elevation of the hill or mountain. This is because the instrument is closer to the base of the hill, which reduces the impact of any errors due to the slope of the terrain.

- Better stability: Setting up the instrument at the bottom of the valley provides better stability, as the ground is flatter and more level. This reduces the risk of the instrument being moved by wind or other external factors, which can cause errors in the measurement.

- Better visibility: Setting up the instrument at the bottom of the valley provides better visibility of the surrounding terrain, which makes it easier to identify any potential obstacles or other features that may affect the measurement.

In contrast, setting up the instrument at the top of the summit (option A) or on one side of the slope (option C) can result in lower accuracy and stability, as well as reduced visibility.

Conclusion

In conclusion, when levelling in an undulating terrain, it is preferable to set up the instrument at the bottom of the valley to achieve the best results. This provides improved accuracy, stability, and visibility, which are essential for accurate measurement of the elevation of the terrain.