Key takeaway
A unit label alone does not say whether a number is an absolute reading, a difference or a procedure-defined score.
Start with the quantity, not the column name
A buyer receives a column called temperature and converts every value by adding 273.15. That works for an absolute Celsius temperature expressed in kelvin. It fails when the column is a temperature rise: a rise of 20 degrees Celsius is a difference of 20 kelvin, not 293.15 kelvin. NIST separates those meanings; UCUM also distinguishes ordinary ratio conversions from offset or function-based conversions.
Before an export, write down what the measured quantity means, how it was produced and what the receiving analysis expects. A pressure ratio, absolute pressure and gauge pressure are different quantities even when their displays use familiar unit labels. Resolving that meaning is a task for the record owner and domain reviewer; a string replacement cannot settle it.
A conversion map with an explicit hold
This hypothetical map concerns internal acceptance testing of three invented fields. Values and conversion decisions are illustrative; they are not observations from a seller archive. Original values remain beside transformed values so a reviewer can reproduce the calculation.
| Source quantity | Original value | Receiving value | Decision |
|---|---|---|---|
| Absolute temperature | 20 °C | 293.15 K | Apply offset; preserve quantity kind |
| Temperature increase | 20 °C difference | 20 K difference | Scale only; do not apply offset |
| Physical length | 2,500 mm | 2.5 m | Scale by 0.001 |
| Procedure-defined severity | Score 7 | No conversion | Hold until the procedure is defined |
Preserve the conversion evidence
For each field, record source and target unit codes, quantity kind, conversion formula, applicable date range, rounding rule and the person who approved the mapping. Retain the source-system label exactly as captured. A later discovery that one system used a different procedure should produce a new mapping version and a scoped correction, rather than silently rewriting the original.
UCUM describes arbitrary units tied to procedures that cannot generally be converted between different measurement methods. In the example, the score stays unresolved because no common measurement procedure has been established. Do not make a conversion coefficient up from the observed range of values. Similar-looking distributions do not establish equal physical meaning.
Test boundaries and precision
Run the proposed mapping on a small synthetic test set before using permitted source records. Include zero, negative values where meaningful, decimal inputs, missing readings and a value close to an acceptance threshold. Check both the expected transformed value and the original quantity label. A reverse conversion can expose some mistakes, but two mutually wrong formulas can still round-trip.
Suppose an instrument reports whole degrees and the export shows 293.150000 kelvin. The extra displayed digits come from formatting, not additional instrument precision. Keep the original resolution and any recorded uncertainty separate from the conversion result. Calibration and uncertainty assessment need their own evidence; this map does not establish instrument accuracy.
- Confirm that a difference field does not acquire an offset.
- Check missing and invalid values before arithmetic; do not convert an unknown reading into zero.
- Compare threshold decisions using the agreed rounding stage and disclose any result that changes.
Approve a bounded receiving contract
Accept the field only when both teams agree on quantity meaning, procedure, unit representation and rejected cases. If the receiving system cannot preserve those distinctions, withhold that field or change the receiving schema. Save the exact map with the evaluation package and ask the buyer to report its version with any result.
This review helps determine whether an authorized export is interpretable. It does not establish ownership, privacy clearance, buyer demand or a license price. The inventory builder can record the unresolved field and the readiness planner can assign the mapping task. Any named introduction, later sample and licensing permission remain separate decisions.