Two ratings can look similar on a cover sheet while describing different evidence. Begin by identifying what was measured, how it was processed and which criterion the project requires. Do not assume a field number is a laboratory product rating or that there is a universal numerical conversion.
| Metric or evidence | Interpretation question |
|---|---|
| STC | Is this a laboratory assembly rating based on transmission-loss evidence, and does the tested assembly match the supplied construction? |
| NIC | Does this describe measured level differences between the selected spaces under the reported conditions? |
| Apparent field rating | Which field method and corrections were used, and how do flanking paths enter the result? |
| Sound Group verification | Does the reported field metric and scope match the approved secure-facility requirement? |
A report-reading exercise
Suppose a supplier provides a laboratory-rated door and a field team later reports a room-to-room result. Those documents do not automatically contradict each other: the field measurement can include the frame, seals, adjoining wall, flanking routes and room conditions. First check the metric and coverage, then investigate the assembly and measurement limitations. This is an illustrative scenario, not an OSAT project result.
Questions to put beside the headline number
- What method and edition were used?
- Which source and receiving spaces were measured?
- What was the installed condition and tested coverage?
- What background or other limitations affected the result?
- What exact criterion is the reviewer applying?
Publisher references include ASTM E336, ASTM E413 and ASTM E90. Use the applicable licensed documents for procedures and calculations; this guide does not reproduce them.
For an initial scope discussion, request testing using unclassified information only. OSAT documents measured performance; the responsible authority makes acceptance and accreditation decisions.