This Helium excuse makes no sense. I know of no pressure testing that involves using Helium...
There are different types of pressure testing, but the 2 types that Omega specifications call for are using a dry pressure testing machine that produces both a vacuum and pressure, and measures the deflection of the case to determine if the watch is leaking. For watches rated more than 100m (the limit of most dry testing machines) then a high pressure wet test is performed at the rated depth of the watch +25%, and this is in addition to the dry testing tests.
The testing is done in several stages, starting with the case empty. First the dry testing machine is used to detect major faults such as pinched gasket, etc. If it passes there, the empty case is put in the water filled testing chamber for 30 minutes at no pressure, then the pressure is raised to 37.5 bar (for a 300 m rated case) for one hour, then back down to zero pressure for 30 minutes - so 2 hours in the water in total. The case is then removed from the chamber, dried off, and placed on a heating unit for 30 minutes. Then a drop of room temperature water is placed on the crystal for 60 seconds, wiped away, and the crystal is checked with a loupe for condensation on the inside of the crystal - no condensation means the watch has passed.
Once the watch is assembled and all timing checks are done, the whole process is repeated with the watch fully assembled.
You say that you are taking it back to the jeweler....do they have a watchmaker on the premise, or are they sending it out? If they are sending it out, ask to be given the contact information for the watchmaker directly, because it's likely the people you are dealing with have no idea how to repair or pressure test a watch.
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