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This article explains that the phenomenon of initially high data readings followed by a gradual decrease in airtightness testing is not due to instrument malfunction, but rather to an improper testing method. The root cause lies in the elastic deformation that occurs when the product is pressurized for the first time; if testing continues without sufficient depressurization and recovery, the stress release process in the material will be superimposed on the leakage values, resulting in a systematic drift in the data. Standard procedures require complete depressurization, allowing sufficient recovery time, controlling temperature, and ensuring fixture consistency; only under these conditions can the repeatability of the equipment be truly evaluated.