Prism Constant Check Calculator
Applies the prism constant to correct EDM total-station distance measurements for the reflector used.
Enter Values
Before you rely on this: First-pass guide only. Verify safety-critical or regulated work against the relevant standards, your project requirements and a qualified professional.
How to use this calculator
- Enter the measured distance.
- Enter the prism constant in millimetres (often −30).
- Press Calculate for the corrected distance.
How it works
Applies the prism (reflector) constant to an EDM measurement: corrected distance = measured distance + prism constant.
Worked example
150.000 m, −30 mm prism. Corrected distance = 149.970 m.
Frequently asked questions
What prism constant should I use?
It must match your reflector and instrument setting — common values are 0 mm and −30 mm. Check the prism's spec.
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Cite this tool
Zerdly. (2026). Prism Constant Check Calculator. Retrieved from https://www.zerdly.com/tools/prism-constant-check-calculator/
Tip: Enter any known values to calculate the remaining results.
All calculations run in your browser. Your inputs are never saved or transmitted.