What is a benchmark and what are its types?

A benchmark (BM) is a fixed reference point of known elevation above mean sea level used as a vertical control for leveling operations. Types include: GTS benchmark (permanent marks established by Survey of India at 1 km intervals along highways), permanent benchmark (established by government on permanent structures), temporary benchmark (established for specific project use), and arbitrary benchmark (assumed elevation for local work). Benchmarks ensure elevation consistency across surveys.