Which of the following statements is/are true for Automatic Levels used for measuring elevations? i. The need for manual adjustments required in the case of dumpy levels to ensure accurate level is eliminated. ii. It uses a compensator mechanism to keep the line of sight horizontal even if it is not perpendicular to the vertical axis. iii. The compensator mechanism made of mirrors or prism is built into the telescope tube and can be activated if the line of sight is horizontal within 15’ – 30’ of the true horizontal.
- AOnly (i)
- BOnly (i) and (ii)
- COnly (ii) and (iii)
- D(i), (ii) and (iii)Correct
Solution
Concept
Operation and features of automatic levels
Formula
NONE
Step-by-step solution
1. Automatic levels utilize an internal compensator mechanism made of mirrors or prisms that automatically maintains a horizontal line of sight within 15’ – 30’ of the true horizontal. 2. This mechanism eliminates the manual leveling adjustments required in traditional dumpy levels. 3. Therefore, statements i, ii, and iii are all correct. Answer: D
Explanation
Automatic levels eliminate the tedious manual leveling adjustments needed in traditional dumpy levels by using an internal compensator mechanism made of mirrors or prisms. This built-in compensator automatically maintains a horizontal line of sight even if the telescope axis is slightly tilted, provided it is within 15 to 30 minutes of the true horizontal. Therefore, all three statements are correct, making option D the correct answer.
Why the other options are wrong
A) Statements (ii) and (iii) are also true regarding automatic levels. B) Statement (iii) is also true for automatic levels. C) Statement (i) is also true as manual adjustments required in dumpy levels are eliminated.
Shortcut
Automatic levels use an internal prism/mirror compensator operating within 15'–30' to level line of sight.
Common mistake
Selecting option B instead of D by assuming statement iii regarding the compensator working range in automatic levels is incorrect.
Correct answer: D) (i), (ii) and (iii)