First we need to understand the DHS fabrication process. DHS uses a batch process, and when working with natural materials like rubber the characteristics will vary some. Things like the quality and ratio of the raw materials in each batch, the tolerances of the machines, the skill of the operator or even the temperature and humidity from that day will influence the results and especially for the sponge, every batch will be slightly different. DHS does not measure every single rubber in a batch. They only measure one or few times per batch and allocate those numbers to the entire batch. So if the measurement was 39 degrees and 2.15mm thickness, they will put all sheets in that batch in the 39 degrees 2.15mm pile. But some sheets in that batch might be 38 or 40 degrees, and some may have a thickness of 2.1 or 2.2mm. Add to that errors that can occur with packing, logistics, labeling and you may end up with something pretty different than what you expected inside the box!