Phonak Naida S UP water resistant rating - IP54

Phonak have emailed me with the water resistant rating for Naida S (not CORE) UP is IP54.

Can anyone explain this? They also told me that the Naida CRT xsp plus is IP67

Which is better?

They state this has been confirmed by submerging aid for 1/2 hour.

OK, I HAVE FOUND OUT THE INFORMATION. THANKS.

Please post.
Depth determines the pressure withstood.

Google ‘Ingression Protection Ratings.’

Thanks
http://www.google.com/search?client=safari&rls=en&q="Ingression+Protection+Ratings"+hearing+aid&ie=UTF-8&oe=UTF-8