The purpose of a 'benchmark' (BM) in surveying is:
Choose the correct answer
Fixing horizontal positions only
Permanent reference point of known elevation (RL above MSL) used as starting point for all levelling surveys
Measuring angles between stations
Storing survey instruments
Correct Answer
B. Permanent reference point of known elevation (RL above MSL) used as starting point for all levelling surveys
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Benchmark: a fixed, permanent point of known elevation above MSL (mean sea level). Established by precise levelling from primary GTS benchmarks (Survey of India). Used as starting point for all height-related surveys. Types: GTS (Great Trigonometrical Survey) BMs (stone/concrete pillars), permanent BMs (brass bolts in walls), temporary BMs (for construction). RL = reduced level above MSL.
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