1. What is your accuracy envelope, and what is it referenced to?
An auditor who quotes a single-figure accuracy (“±2%”) without specifying reference ground truth is describing a claim, not a method. A defensible answer names the reference — weighbridge throughput, calibrated pile, or sealed control volume — and the statistical basis for the envelope (standard deviation over n cycles).
2. How do you reconcile volume to tonnage?
Volume is measured. Tonnage is derived. The derivation uses a bulk-density assumption that varies with moisture, compaction, and material. If the auditor uses a constant bulk density year-round, they are either adding error they cannot quantify or they have a calibration regime they should be able to produce on request. One of those is acceptable.
3. What is your base-surface (toe polygon) definition protocol?
Volume is the difference between the measured top surface and a defined bottom surface. If the bottom surface is redefined between cycles, phantom volume appears or disappears — not because the pile changed, but because the reference did. The answer should be a written protocol: which polygon, surveyed when, locked against what reference.
4. Where is the weighbridge reconciliation table?
Every measurement cycle should produce a reconciliation table: opening measured tonnage + weighbridge inflows − weighbridge outflows = expected closing tonnage. Compared against the actual closing measurement. Residual flagged if it exceeds tolerance. If the auditor does not routinely produce this table, they are operating in an open loop.
5. If I re-survey the same pile the same day with a different crew, what do I get?
This is the repeatability test. Methods that are internally consistent produce results within a narrow spread when re-measured. Methods that rely on individual expertise do not. Ask for the re-survey test to be run at your next cycle. If the auditor declines, the test answers itself.
The close
A measurement regime that passes these five tests produces a closing inventory number that your auditors will accept, your auditors’ auditors will accept, and your working-capital financiers will discount less aggressively. A measurement regime that does not pass them is producing a number that looks like data and functions like a negotiation.
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