Hmmmm.... Actually, I hadn't thought of that. So for those of you who dive with pony or stage bottles (I haven't yet), you carry them charged, with the valve off, and check periodically during the dive to be certain the pressure is holding? I assume this is to prevent water intrusion into your first and second stages? Is loosing charge a frequent issue?If the purge button got bumped or for some other reason the second stage allowed some or all of that charge to bleed off would you know by glancing at your button spg?
I was thinking they could be useful on a bailout bottle (or argon in the future) to confirm air and charge prior to entering the water. In the water, well, a bailout bottle only has enough air for an immediate direct ascent to a safety stop... I wonder if the exact pressure beyond what you can estimate from experience and/or the little SPG really makes any difference in that situation???
Still, why not use a regular SPG on a 6" hose??? I guess the only answer left is that it looks cleaner. Functional vs. looks good... hmmmm... maybe what I really need to do is start looking for a 6" hose
