The nines after the decimal point indicate the precision of the device, which is used in laboratories to measure the removal of micro-organisms – and therefore its limitations as well.
For certain pests visible to the naked eye or under the microscope, a 100% elimination rate can be achieved as there are no restrictions.
Every 9 achieved is a massive advancement because it means a higher level of removal. For example, a 99.99% removal of micro-organisms is 10 times greater than a 99.9% removal. So, with one extra 9, bacterial residue goes from 1/100 to 1/1000. For micro-organisms such as bacteria, viruses and fungi, it is especially important to achieve the highest possible removal rate.