B.R.M FF39-40 Notice D'utilisation page 8

Water-resistance
Your B.R.M Chronographes watch is waterproof up to 30 meters. This
indication is engraved on the back of the case it corresponds to the
current norms of the watch-making industry. The measurements have
been carried out by application of pressure and depression.
The maintenance of the waterproof characteristics of your watch depends
on the care you will bring to it.
Before any contact with water, make sure the winder is in position 0.
Maintenance
The maintenance or repair of your B.R.M Chronographes watch must be
carried out exclusively by a B.R.M Chronographes authorized dealer.
brm-chronographes.com