En 50147-1 Pdf [new] Here

The shielding attenuation is: [ a = P_\textref - P_\textmeas \quad (\textin dB) ]

To identify areas of potential RF leakage in the shielding structure. Scope and Frequency Range en 50147-1 pdf

EN 50147-1 is a European standard specifically designed for the measurement of shielding effectiveness The shielding attenuation is: [ a = P_\textref

Because EN 50147-1 is a copyrighted harmonized European standard, it is not legally available for free public download. To obtain a legitimate, official PDF copy, you must purchase it through authorized standards organizations. official PDF copy

Following the PDF ensures that tests can be repeated and validated, which is important for quality control in chamber manufacturing.