I've had a Calypso VI. It is literally a Calypso IV with the recall bushing installed, a swivel for low pressure hoses, and a different sticker.
It's USD. It's either a Calypso, an Aquarius, or a Conshelf on the inside. If you get really lucky then it is a 1960-1965 regulator, and some of those were unique. Everything after 1970 is a repackaged version of something that has already been done. Heck, the Titan that AQ sells right now is a conshelf
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