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how many the least reading for angles can be measured by vernier theodolite ?
1''
10''
20''
20'
20''
A vernier theodolite is a surveying instrument designed for measuring horizontal and vertical angles. The least count of a standard vernier theodolite typically ranges from 20" to 60", with 20" being the most common precision found in engineering curriculum and field practice.
A vernier theodolite is a surveying instrument designed for measuring horizontal and vertical angles. The least count of a standard vernier theodolite typically ranges from 20" to 60", with 20" being the most common precision found in engineering curriculum and field practice.
LC=nS — where LC is the least count, S is the main scale smallest division, and n is the number of vernier divisions.
The principle involves the comparison of two scales: the main scale and the vernier scale. The least count is determined by the formula LC=nS, where S is the smallest division on the main scale and n is the number of divisions on the vernier scale. By aligning the graduations, the instrument achieves a precision higher than the resolution of the main scale alone.
The least count represents the smallest angle that can be measured directly without estimation.
Vernier theodolites are mechanical instruments and are less precise than modern electronic digital theodolites (which can reach 1").
Precision is inversely proportional to the complexity of the vernier scale alignment.
Economical for basic surveying tasks.
Robust mechanical construction suitable for harsh field conditions.
Susceptible to human reading errors (parallax and interpolation).
Lower precision compared to optical or digital micrometer theodolites.
Topographic surveys.
Laying out traverse lines.
Theodolite traversing for civil engineering works.
Option D (20') is incorrect as it represents a value in minutes, which is far too coarse for standard angular measurement requirements in surveying.
While some high-precision vernier theodolites exist, 20" is the industry-standard benchmark for the least count in examinations.
C is correct — The standard least count for a conventional vernier theodolite used in surveying is 20".
Always remember that in surveying instruments, the 'Least Count' is the smallest value the vernier scale can reliably distinguish on the main scale graduations.