Benchmarks
A benchmark is a permanent reference point relatively, the elevation of which is known (assumed or known w.r.t. MSL). It is used as a beginning point for levelling or as a point upon which for a check to close. Different types of benchmarks used in surveying are following:
(1) GTS benchmarks
(2) Permanent benchmarks
(3) Arbitrary benchmarks and
(4) Temporary benchmarks.