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Doubles are not available in many places. With a sidemount rig you can assemble a technical rig anywhere in the world you can find two scuba tanks.
I like being able to breathe 3000 psi on the first dive and still have 3000 to start the second.
You mean like a single tank on the back and then a fresh single tank on the back for a second dive?
Sorry Stu, what I mean is there is no need to sacrifice gas for reserve, you can breathe both cylinders down to half and still have the equivalent of a full cylinder left.
Just split the reserve for dive 2 between both cylinders.