Combination of test results

When lots of wool are combined into a larger delivery, combination certificates are often required to cover the consignment. These are simply the result of mathematically calculating the properties of the consignment based on clean mass weightings. The calculations are fully defined in IWTO-31, and no further testing is involved (other than that in the original component certificates). Combination certificates are much more precise than individual certificates because of the averaging process.

The following table gives some indications of the improvement in precision of certification of raw wool consignments obtainable by combining lots:

Occasionally problems are encountered meeting specifications when scoured outputs are predicted using combination calculations on the greasy inputs. Info-bulletin 4.4 outlines some of the issues.