Today, I continued my examination of respiratory protection equipment. I observed significant discrepancies between the data from a fit testing device and a particle counter. For instance, when testing the AirFanta 4Lite at a distance of 0cm with the "L" speed setting, the particle counter indicated a protection rate of 50, while the TSI 8020 reported a fit factor of approximately 6.5. At a distance of 30cm with the same speed setting, the particle counter showed a protection rate of 14, and the TSI 8020 indicated a fit factor of about 4.3. @gerard, obtained similar readings. I acknowledge that particle counters and fit testing devices operate differently. Particle counters directly measure particles larger than 0.3 microns, whereas fit testing devices use isopropanol to pre-treat the particles. However, the crucial question everyone is asking is: which measurement is more reflective of real-world protection against pathogens like COVID-19? I can offer some insight on this matter. Last year, a certified laboratory, "Guangzhou Institute of Microbiology Group Co., Ltd, National Center of Quality Inspection and Testing on Air Purification Products," conducted a germ filtration test on the 4Lite model, following the GB/T 5365-2019 standard. The test assessed the density of microorganisms at the filter's entrance and exit. They used "Staphylococcus albus" bacteria and "H1N1" virus for the tests. The average filtration rate for Staphylococcus albus was 98.42%, corresponding to a protection factor of 63. For H1N1, the average filtration rate was 99.51%, equating to a protection factor of 204. From these results, it's evident that the actual protection factor against COVID-19 and other pathogens is significantly higher than what fit tests and particle counters suggest. Both N95 respirators and the 4Lite device provide much greater protection than fit test results might indicate.