Inherent soil variability Sufficient number of tests can minimise this error. Sampling error Correct size sample/type of sampler to account for soil structure

and sensitivity. In situ testing for granular material. Measurement error Not all test results from even accredited laboratories should be

used directly. Sufficient number of laboratory tests to show up “outliers”. Understand limitation of the tests. Validate with correlation tests. However appreciate significant variation in correlations.