Survey Measurement, Instrumentation and Adjustment
Measurement and adjustment
This domain tests instrument use, error theory, redundancy and adjustment. Accuracy is closeness to truth; precision is repeatability. Random errors are treated statistically; systematic errors such as prism constant, collimation, refraction or scale error must be eliminated or modelled. Adjustment distributes inconsistent observations but cannot cure blunders or systematic bias.
Core rules
- Calibrate and check instruments; record prism constant and atmospheric corrections.
- Use redundancy: closed traverses, repeated observations, independent checks.
- Apply least squares or accepted approximate methods only after blunder detection.
- Keep units and significant figures consistent.
- Report misclosure and the adjustment method.
Worked example
A closed traverse of 300 m has a linear misclosure of 0.030 m. The relative misclosure is 0.030/300 = 1/10,000. If the specification requires 1/5,000, the survey passes; if it requires 1/20,000, it fails and must be reobserved. A Bowditch adjustment may then distribute the misclosure, but only after checking for gross errors. The reasoning is that adjustment is justified by acceptable misclosure, not used to hide a bad observation.
Traps
Treating systematic error as random; adjusting before finding a blunder; ignoring prism constant; mixing degrees and grads; and over-weighting one measurement without justification.