When the level is near P, the reading on P is 2.165 m and on Q is 3.810 m. The difference in this setup is:
Difference 1 = 3.810 m - 2.165 m = 1.645 m
When the level is moved near Q, the reading on P is 0.910 m and on Q is 2.355 m. The difference in this setup is:
Difference 2 = 2.355 m - 0.910 m = 1.445 m
The average of the two differences gives the true difference in level between P and Q:
True Difference = (1.645 m + 1.445 m) / 2 = 1.545 m
The computed true difference in level is 1.545 m. This value must fall within the given range of 1.54 to 1.55 m, which it does:
1.540 ≤ 1.545 ≤ 1.550
Important Questions from Levelling Methods
- Which one of the following is the purpose of taking a backsight observation in levelling?
- The observations of a reciprocal levelling operation carried out from two stations A and B are given in table. It is known that the instrument has collimation error. The correct staff reading over station B when the instrument is set very near to station A is ________ m (Rounded off to three decimal places).
Assume all other errors are negligible.Staff readings at station Instrument set very near to station A (m) B (m) A 1.275 2.005 B 1.040 1.660 - A level with the height of the instrument being 2.550 m has been placed at a station having a Reduced Level (RL) of 130.565 m. The instrument reads 3.665 m on a levelling staff held inverted at the bottom of a bridge deck. The RL of the bottom of the bridge deck is __________ m (rounded off to 3 decimal places).
- Change Point (CP) in levelling refers to a location where
- At a fixed instrument location in levelling, if the backsight reading at a point P is more than the foresight reading at a point Q, then
