Here are a couple of true "blasts from the past" -- finally rescued from my dismal Bay Area storage unit, which had always reminded me of the "Your Self Storage," from The Silence of the Lambs.
Among them, is a "Barakuda - Cyklomat," produced by Poseidon / Aqua Sport, some five decades ago, for the German company, Barakuda; and the second, one of the earliest models of the Cyklon.
Both of those very simple first stages only allowed for the use of a single second stage, pre-dating any use of submersible pressure gauges, by several years; and, aside from a notable lack of a purge button and the presence of a metal ejector sleeve, the "guttiwuts" of that fully metal Cyklomat, are nearly identical to that of any modern Cyklon.
The "connection wheels" on both regulators, were stamped "Aqua-Sport" of Göteborg, Sweden, a name which briefly preceded the use of the brand, "Poseidon" . . .