Surveying
Benchmark
A permanent reference point of known elevation used by surveyors and engineers to establish vertical control on a project.
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In the Field
The project benchmark is established by a licensed surveyor and usually ties to a USGS benchmark or established city datum. All field elevation checks on the project trace back to this single reference point. Guard it — if it gets knocked out, the surveyor has to reestablish it.
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Rule of Thumb
Always have at least two benchmarks on a project — if one is disturbed, you can check the other. Use concrete monuments or substantial steel stakes in protected locations.