The splitting tests are used for estimating a trees stability when sawn (wet), using an estimated strain as a numerical indicator. Due to the inhomogeneity of material properties properties around the stem, the orientation of the cut measures a result which will differ from a measurement taken from a different orientation. However the value of the splitting tests is the speed at which they can be conducted, so the test can only be conducted once per sample (the destructive nature of the testing procedures also precludes repeated measurements), and this number is used as a proxy for the value within the whole stem, and consequently the trait value of the individuals genetics. It is important to know how well this estimate performs, and the proportion of error associated with the orientation as oppose to random measurement error. error. The four tests used here all measure the 'same' property, in that they are all numerical proxies of how much a sample is likely to deform when it is green sawn and consequently should all give the same result. The first three tests (original, rapid, quartering (same plane)) should provide the same numerical result for each sample. Differences between them can only be due to the testing procedure as they measure the same plane. The final test (quartering (perpendicular plane)) compounds measurement error (which will be the same as the quartering (same plane) test) with error resulting from measuring a different orientation of the sample. By comparing these test results over multiple samples an estimate of how much error is associated with each measurement was produced. Note that although we call the numerical result 'strain', it is not a measure of the same sample property as when a strain gauge procedure is used. The 'strain' measurements from splitting tests and strain gauges or the CIRAD method do not measure the exact same thing, and are not directly comparable. Strain guages measure the surface strain over over a given small area, while the splitting test measures a non-uniform consolidation of the three dimensional strain field. Strain, in the sense it is used here is the name given to the numerical proxy for how much deformation can be expected during green sawing of a sample obtained from the splitting tests.
Equations \ref{eq:prec_min_1} to \ref{eq:prec_min_6} were solved simultaneously to estimate approximate measurement error on each test, and the error resulting from the rotation of the sample. Table \ref{618809} shows the mean and 2nd standard deviation (95% confidence interval) of the theoretical error distributions. In these cases, the mean indicates a systematic error, while the 95% confidence intervals are random error associated with that measurement type (i.e. measurement error).