NSPS CST Level III key terms

A fixed, known elevation or horizontal position used as a reference for comparing subsequent survey measurements. Establishing and preserving benchmarks allows later crews to detect movement or confirm that construction matches design.

A reference surface or reference frame to which positions and elevations are tied. A vertical datum defines zero elevation, while a horizontal datum defines the coordinate system, so mixing datums shifts every computed value.

A set of monumented points with known coordinates that anchors all subsequent survey work. Densifying from control rather than from isolated points keeps measurements consistent and lets errors be traced to a common reference.

A survey route in which a series of connected lines and angles is measured to determine coordinates of successive points. Open traverses lack a check at the end, while closed traverses allow misclosure to be computed and adjusted.

The difference between a measured value returning to a known point and that point's known value. Small closure indicates consistent work; excessive closure signals blunders or systematic error that must be found before the survey is accepted.

The amount by which the sum of measured interior or exterior angles of a closed figure differs from the geometrically required sum. It is compared against an allowable tolerance based on instrument precision and number of angles turned.

An instrument combining an electronic theodolite with an electronic distance meter and onboard computing. It measures horizontal and vertical angles plus slope distance to a target, then computes coordinates and elevations in the field.

A sight taken to a point of known position to orient the instrument and establish the reference direction for subsequent angles. A wrong backsight rotates every following shot and is a common source of systematic error.

A sight taken to a point whose position is being determined, or in leveling the last reading before the instrument is moved. Foresight readings are subtracted from height of instrument to obtain the new point's elevation.

The elevation of the instrument's line of sight, computed by adding the backsight reading to the known elevation of the point occupied. Each new foresight elevation is found by subtracting its rod reading from this value.

The process of determining elevation differences by reading a graduated rod through a level from two or more instrument setups. Running the loop back to the starting benchmark produces a misclosure that shows whether the work is acceptable.

A correction applied for the offset between the prism's reflective surface and the point it represents, plus any instrument-specific offset. Entering the wrong constant shifts every measured distance by a fixed amount.

A repeatable bias that shifts measurements in the same direction, such as an incorrect prism constant or an out-of-adjustment instrument. It does not average out with repeated readings, so it must be identified and corrected.

Unpredictable variation in measurements caused by instrument limits, atmospheric conditions, and observer judgment. It tends to cancel when many observations are averaged, so redundancy is the main defense against it.

A gross mistake such as a misread rod, transposed digits, or a sight taken to the wrong point. Unlike random error, a blunder is not reduced by averaging and usually shows up as a large closure failure.

The station where the instrument is set up, with coordinates entered or assumed for that setup. Its position and the orientation established from it govern the accuracy of every measurement taken from that setup.

The equipotential surface of the Earth's gravity field that approximates mean sea level and serves as the basis for orthometric heights. Its undulation relative to the ellipsoid is needed to convert between ellipsoidal and orthometric elevations.

A mathematically defined, smooth model of the Earth's shape used as the reference surface for geodetic coordinates. GNSS-derived heights are ellipsoidal and must be converted to orthometric heights for most construction and drainage work.

Elevation measured above the geoid, roughly equivalent to height above mean sea level. It is the elevation used on construction plans and for gravity-driven flow, unlike raw ellipsoidal height from satellite positioning.

A set of projected coordinate systems defined for each state so that local coordinates remain nearly distortion-free. Projects tied to it must record the zone and datum used, since coordinates from different zones are not interchangeable.

A mathematical transformation that converts positions on the curved Earth to a flat coordinate grid. Every projection introduces scale distortion, so the map projection and its scale factor must be documented with the survey.

Satellite-based positioning that computes receiver coordinates from signals of multiple orbiting satellites. Field use requires clear sky view and awareness that reported heights are ellipsoidal, so a geoid model or local benchmark check is needed.

The field operation of marking planned points, lines, or grades on the ground from design coordinates. Accuracy depends on the control used, the instrument setup, and checking staked positions against an independent reference.

A record of actual constructed locations and elevations, measured after installation rather than taken from design drawings. It documents deviations, supports payment, and feeds future tie-in work and record drawings.

The permissible range of variation from a specified dimension, elevation, or alignment before work is rejected or corrected. Tolerances should be stated in the specification and matched to the precision the field methods can realistically achieve.

The written project requirements defining materials, methods, testing, and acceptance criteria that the contractor must meet. Field staff must read the governing specification sections because they control what is inspected and what constitutes acceptance.

A document or product data package the contractor sends to the designer for review and approval before installation. The review confirms conformance with the design intent, and approved submittals become part of the project record.

A detail drawing prepared by the contractor or fabricator showing how a component will actually be built and installed. It translates design drawings into fabrication detail and must be checked against dimensions and specifications before approval.

A formal written question from the contractor asking the designer to clarify conflicting, missing, or ambiguous information. Timely, well-documented responses prevent rework and may later support a change order or schedule adjustment.

A written modification to the contract that adjusts scope, price, or time, signed by the authorized parties. It must be issued before the changed work proceeds, because verbal direction alone gives no basis for payment.

The contractor's periodic request for payment based on work completed and materials stored. It is typically supported by a schedule of values and verified by field observation before the owner approves the amount.

A breakdown allocating the contract price across work items, used to measure progress for each pay application. It must reflect actual relative value, or payments will not track the work installed in the field.

A compiled list of incomplete or defective items identified near substantial completion that the contractor must correct. Closing the list is normally required before final payment and release of retainage.

The stage at which the work is sufficiently complete for the owner's intended use, even though minor items remain. It usually starts warranty periods, shifts risk of loss, and triggers release of a portion of retainage.

A percentage of each payment withheld by the owner until the work is substantially or finally complete. It protects the owner against incomplete or defective work and is released according to the contract terms.

The owner's formal acknowledgment that all contract requirements, including punch list items and closeout documents, have been satisfied. It typically follows substantial completion and precedes final payment and retainage release.

A scheduling technique that identifies the longest sequence of dependent activities, which determines the project's minimum duration. Delays to activities on that path push completion, while float on other activities absorbs slippage.

The amount of time an activity can slip without delaying the project completion date. Knowing which activities hold float helps the team decide where to absorb delays without triggering a schedule claim.

A pre-agreed sum the contractor owes the owner for each day of late completion, representing anticipated owner losses. The amount must be a reasonable forecast rather than a penalty, or courts may decline to enforce it.