What is the key difference between the Rise and Fall Method and the Height of Instrument (HI) Method in levelling?
- AThe Rise and Fall Method requires only one reading per station, while the HI Method requires two readings per station.
- BThe Rise and Fall Method determines the elevation changes between consecutive points, while the HI Method calculates the elevations by referencing the height of the instrument.Correct
- CThe HI Method is more accurate than the Rise and Fall Method for long distance levelling.
- DThe Rise and Fall Method uses the foresight directly for elevation calculation, while the HI Method uses backsight readings only.
Solution
Concept
Comparison of levelling computation methods
Formula
NONE
Step-by-step solution
1. The Rise and Fall Method calculates relative elevation differences between consecutive stations directly. 2. The Height of Instrument Method calculates elevations by determining the instrument height using backsight readings. Answer: B
Explanation
The Rise and Fall method determines the differences in elevation by directly comparing consecutive staff readings to see whether the ground rises or falls between adjacent stations. In contrast, the Height of Instrument method calculates the plane of collimation height first and subtracts subsequent intermediate and foresight readings from it to find ground elevations. Thus, option B accurately describes the fundamental difference between these two leveling methods.
Why the other options are wrong
C) Height of Instrument method is not inherently more accurate than the Rise and Fall method for long distances. D) The Rise and Fall method does not use foresight directly without intermediate readings nor does HI use backsight readings only.
Shortcut
Rise & Fall compares consecutive points; HI Method references height of instrument.
Common mistake
Selecting option A or D by confusing how consecutive staff readings and instrument height are utilized in the Rise and Fall versus HI methods.
Correct answer: B) The Rise and Fall Method determines the elevation changes between consecutive points, while the HI Method calculates the elevations by referencing the height of the instrument.