Question:
The least count of a self-reading levelling staff is
The least count of a self-reading levelling staff is
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The least count of a levelling instrument refers to the smallest value that can be accurately read.
For a self-reading staff, this is typically 5 mm, i.e., 0.005 m.
Updated On: May 27, 2025
- 0.5 mm
- 0.15 cm
- 5.0 cm
- 5.0 mm
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The Correct Option is D
Solution and Explanation
Step 1: Understanding the levelling staff.
A self-reading levelling staff is a graduated staff which is read directly by the surveyor using an optical level. The smallest division on the staff determines its least count.
Step 2: Standard least count.
Most self-reading levelling staffs are graduated in 5 mm intervals.
Hence, the least count is \( \boxed{5.0 \text{ mm}} \).
Step 3: Eliminate incorrect options.
(1) 0.5 mm: too fine for a staff marking.
(2) 0.15 cm = 1.5 mm: again, finer than usual graduation.
(3) 5.0 cm = 50 mm: too coarse.
A self-reading levelling staff is a graduated staff which is read directly by the surveyor using an optical level. The smallest division on the staff determines its least count.
Step 2: Standard least count.
Most self-reading levelling staffs are graduated in 5 mm intervals.
Hence, the least count is \( \boxed{5.0 \text{ mm}} \).
Step 3: Eliminate incorrect options.
(1) 0.5 mm: too fine for a staff marking.
(2) 0.15 cm = 1.5 mm: again, finer than usual graduation.
(3) 5.0 cm = 50 mm: too coarse.
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