One last question concerning solids properties concerns new solids whose properties have not been investigated before. The test procedure can only identify the properties of the chosen sample. The design must cope with variations in properties which will occur over the life of the structure. A stochastic extrapolation system is needed for bulk solids which have not yet been tested. The drafting committee for the Australian code , tried to address this matter, but the inherent variability of a material is difficult to assess. The method must cope with the practical situation: the only sample may be yesterday's production which may be atypical; the plant to produce the solid may not have been built yet, so the sample may differ significantly from the final form; the coal which is being tested may come from the seam which is the chief goal of the mine, but others with different properties may be mined in the future. It is unusual for plant and mine designers to appreciate these niceties of silo design.