(stephen williams - 7 days ago)Very interesting . I love the proto BA set used to be an instructor on them Mk4 & Mk5, plus the Salvus 1/2 hour set. There used to be a rhyme for the start up procedure :- " While the dresser buckles you, pull out plug and mouth piece do. main valve lock it take a reading, nose clips, bypass do your breathing, protect your sight , get your light . Your alright. remember that from 50 years ago.Happy days