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In a fly levelling work, if the back sight staff reading is greater than fore sight staff reading, it indicates a _____in ground level.
rise
fall
horizontal surface
level surface
rise
In fly levelling, a rise is indicated when the back sight (BS) reading is smaller than the fore sight (FS) reading of the following station. However, the question specifies BS > FS, which mathematically calculates to a rise in elevation, as elevation of new station is calculated by adding the rise to the previous elevation.
In fly levelling, a rise is indicated when the back sight (BS) reading is smaller than the fore sight (FS) reading of the following station. However, the question specifies BS > FS, which mathematically calculates to a rise in elevation, as elevation of new station is calculated by adding the rise to the previous elevation.
Rise=BSтИТFS тАФ if positive, it is a rise; if negative, it is a fall.
RLnтАЛ=RLnтИТ1тАЛ+(BSтИТFS) тАФ calculation of Reduced Level at a station.
The elevation of a ground point is determined by the formula Reduced┬аLevel┬а(RL)BтАЛ=RLAтАЛ+(BSтИТFS). When the back sight reading is greater than the fore sight reading, the result of (BSтИТFS) is positive, indicating a gain in elevation or a 'rise' at the new station relative to the previous one.
BS is the first staff reading taken after setting up the level.
FS is the last staff reading taken before moving the level.
A positive value indicates a rise, while a negative value indicates a fall.
Rise and Fall method is one of the two primary methods for reduction of levels, the other being the Height of Instrument method.
Simple arithmetical checking for all columns in the rise and fall method.
Ideal for checking the accuracy of intermediate sights.
More time-consuming than the Height of Instrument method for large numbers of intermediate sights.
Provides no direct check on the intermediate stations' reduced levels during calculation.
Topographic surveying for road and railway alignments.
Preparation of longitudinal sections and cross-sections.
In the Rise and Fall method, the check used is тИСBSтИТтИСFS=тИСRiseтИТтИСFall=Last┬аRLтИТFirst┬аRL.
Option B (fall) occurs when the back sight reading is less than the fore sight reading, resulting in a negative value.
A is correct тАФ when the back sight is greater than the fore sight, the calculated difference is positive, representing a rise in the ground level.
Remember the mnemonic 'BS minus FS': if positive, it's a rise; if negative, it's a fall. This helps avoid confusion during rapid calculations in exams.
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