Another thing - many divers using vintage equipment prefer the J valve and will not run an SPG because they want to remain period correct in everything - That means no SPG on their gear and when the reg gets a little labored to breathe off of, you pull down the J valve and go into reserve to immediately begin your controlled ascent.
These are very experienced divers and can easily gauge their air consumption because they are well trained and are paying attention to their bottom time, depth, tank size, WOB on any particular dive and so forth. As well, They're all (mostly) using steel tanks and can accurately gauge their tank pressure by the buoyancy swing they are going to feel as the tank drains down.
If I'm diving a steel tank that I'm familiar with, or even somewhat familiar with, I will know to within 100 psi when I have a half a tank remaining because I can feel the swing.
Many divers in the misty days of diving past did not trust the "new" submersible pressure gauge because popular diving mythology held that the SPG was unreliable and tended to explode and spray glass and oil all over the deck when they did.
Whatever the truth is, I have never seen an SPG explode (hose ruptures, yes) when brought to full tank pressure and I like having something to look at besides fish so I always run an SPG even on diving equipment I use from the 50's and 60's -
I recommend you use an SPG until you're comfortable enough to feel that it isn't a required piece of your kit - which may be never.
If you'd like to sell that doubles manifold, there are plenty of interested people (buyers) around
Six of one and a half-dozen of the other, please.
