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
For the traverse given below, the benchmark is at ground point L. The Reduced Level (RL) of L is 150.000 m. The direction of the traverse is from L to N. The readings on levelling staff using the same levelling instrument kept at Stations S1 and S2 during the traversing are shown in the figure.
Column 1 Column 2 (P) 3.300 m (I) Sum of Back Sights (Q) 2.500 m (II) Sum of Fore Sights (R) 150.300 m (III) RL of Point N (S) 3.000 m (T) 150.500 m Matching the information given under Column 1 and Column 2, which one of the following options is CORRECT?
Which of the following errors can be eliminated by reciprocal measurements in differential leveling?
I. Error due to earth curvature
II. Error due to atmospheric refraction
Which of the following is the CORRECT ratio of refraction correction to curvature correction?
The following sights are taken on a “turning point”
If the bench mark is 560.50 m. and height of instrument is 561.365 m. then, what will be back sight ?
