The Dacor Diving Lung Dial a Breath was a 2 stage double diaphragm design. This double diaphragm design was used to circumvent the Cousteau Gagnan patent from what I am told. I have not dived this one, but did dive a Dacor Diving Lung for several years in the late 90s. I found it to be a good breather, though many people would disagree with that statement. My only 2 complaints with this regulator is that it sits a little too far forward and the hoses, while very strong and not prone to breakage, were very stiff, short, and uncomfortable, owing to the belting in them. Positives in favor of this design was no duckbill, screws instead of c clips or clamps and a robust yoke.