The class is written as an ISO Class number N; for each considered particle size the maximum permitted concentration, in particles per cubic metre, is read from the standard's Table 1, where the concentrations are cumulative (a limit at one size includes all larger particles). The table marks the combinations of class and size where classification is inappropriate because of sampling and statistical limits at low concentrations, particle losses for larger sizes, or very high concentrations, and ISO Class 9 applies only in the operational state; the table's figures are criteria for classification and do not represent the real size distribution of particles in the air.
The graph holds this control, the 0 it maps to, and the evidence behind each claim, over MCP and REST.