Identify the correct statement(s) about a change point in a levelling operation. Statement I : It is also known as turning point. Statement II : The plus sight is taken on the change point on one set of instrument to ascertain the elevation of the point. Statement III : The minus sight is taken on the change point to establish the new height of the instrument.
Statement I and III only
The question is asking about the correct statements regarding a change point in a levelling operation. Let's evaluate each statement:
- Statement I: It is also known as turning point.
This statement is correct. In levelling operations, a "change point" is commonly referred to as a "turning point." It is a point where the level of the instrument is changed while keeping continuous levelling operations.
- Statement II: The plus sight is taken on the change point on one set of instrument to ascertain the elevation of the point.
This statement is incorrect. At a change point, a plus sight is not taken to ascertain the elevation. Instead, a minus sight is usually taken on the backsight rod (on the CP) to determine the height of the instrument, and the foresight rod reading is used to transfer this height to the next setup.
- Statement III: The minus sight is taken on the change point to establish the new height of the instrument.
This statement is correct. The minus sight (backsight) reading is taken on the change point to establish the new height of the instrument (HI). After setting up the instrument at the new location, the HI can be calculated by adding the backsight reading to the known elevation of the change point.
Thus, the statements that correctly describe a change point in levelling operations are Statement I and III.
Important Questions from Levelling
Calculate the true reduced level (m) of a point A after correcting the refraction and curvature. The staff reading at the point taken from an instrument set at a distance of 2 km from the point A is 2.56 m. The staff reading from the same station on a bench mark of reduced level is 100 m is 1.34 m.
The dumpy level is most suitable for levelling survey:
Levelling in which staff and readings and the distance between the points is required is called:
Which level has internal compensator mechanism to automatically adjust the line of sight?
Bench mark is established by -
