The document discusses the ISO 4406 standards for particle counting, which specifies particle counts per milliliter within set size ranges. It provides a table showing the scale numbers and corresponding particle count ranges. The ISO 4406 code uses one, two or three scale numbers separated by slashes to indicate the particle count for different size ranges, with the largest particle size range listed first. Examples are given of 2 and 3 code particle counts and their corresponding ISO codes.