To go into interpreting water resistance measurements would be to dive deep (pun intended) into ISO standards and what not, far too much time to be investing into it IMHO. The % of the leak rate is basically a measure of the deformation of the case against the applied pressure and of course there's a limit, which is different for watch case sizes and of course depth. Ideally it should be zero, but as the pressure inside the watch case is not equalized to the pressure applied to the outside and the watch is not perfectly sealed, that's an impossibility (which is why the term waterproof ceased to be used as there is no such ideal model,eventually at some point, everything leaks). So there is a limit to how much leaking or deformation that can happen in a specific amount of time. That's why instruments such as the one bought by TDs are used, to take the measurement and do the calculations instantly. As much as there is data presented to you, I still would advise you against using your watch in water unless it has been tested at your local watchmaker. I don't think there is a TD which guarantees the watches from water damage, they just do the WR test as an added service, nothing more.
