Strength groupings can be assigned as either a positive strength grouping or a provisional strength grouping. A positive grouping can be assigned on the basis of small clear specimens to determine mechanical strength properties for five or more trees. The samples must achieve a distribution of values which represent the distribution of values in the population, and must be free of bias. A provisional strength grouping is assigned on the basis of density or limited mechanical testing data. Provisional strength grouping are assigned when mechanical testing results are from limited sampling, or sampling that does not represent the characteristics of the parent population. Provisional strength groupings are conservative and desirably so, because of the predictive relationships in making the assessment.

A classification, either positive or provisional is determined by comparing the species mean (average) value of modulus of rupture, modulus of elasticity and compression parallel to grain, with minimum values listed for each strength group in the standard AS 2878.

The classifications indicated in 3.1.2 and 3.2.2 of this report are assigned on the basis of a preliminary positive classification. The sample number in this study was fifteen billets from different trees, which satisfies the minimum requirements for positive strength groupings. A positive strength grouping requires that the sample is free of bias and representative of the larger population. These assumptions may not be valid for this study as the samples were collected from a limited area. It may therefore be more correct to assign provisional strength groupings. The method of assignment is the same as for positive strength groupings, however the classification is lowered by one strength group and in reporting, the strength grouping is placed in brackets to indicate that the grouping is provisional. If provisional strength groupings were used in this study the groupings would be S7 for the unseasoned material and SD8 for the seasoned material.