This is used to test the efficacy of the air removal system and that the hydraulic system is perfectly air-tight. The test is defined according to EN 13060, which lies down that there must be a cycle that carries out this test automatically on all autoclaves that have a vacuum phase for removing air. For this test at least the vacuum phase is carried out as in the highest performing cycle offered by the machine, then the chamber is kept in isolation for a certain length of time and the increase in pressure due to any re-entry of air is checked to make sure it is lower than a pre-defined value.