Cleanliness factor is represented by 3 models. One of them is already introduced [FED-STD-209 (American Federal Standards)], followed by [JIS B 9920 (Japanese Industrial Standards)] and [ISO (International Standard Organization) regulations]. Traditionally, the [FED-STD-209D] standards were implemented. However, due to unification to International System of units (SI units), the clean factor regulations are also switched to ISO standards and the usage of American Federal Standards is discontinued since 2001. However, the implementation of [FED-STD-209D] is still practiced and will take some time to completely adopt the ISO standards.