Marking
3.4. A hydrostatic release unit shall be marked permanently on its exterior with a means of identifying its type, serial number, depth at which it will release, and in addition if a type which;
3.4.1 requires servicing with its date of manufacture and a small plate permanently attached to the unit for recording the date of servicing;
3.4.2 is disposable, with the date at which it must be replaced.