Looking at pictures of a Contessa-Nettel/Zeiss Ikon Steroco camera that has the Compur Stereo shutter. On the left is the normal shutter speed dial, but what does the other one do? The only marking I can see is the F. Deckel logotype. The aperture and focus is set by levers.
Is the mystery wheel turned to unlink that shutter for taking single photos? But it's a plate camera, so that wouldn't make sense unless you used a rollfilm cassette.
On some versions of the Compur Stereo, one wheel is for aperture and the other for the speed. Another version has the wheel for shutter speeds only. It makes me wonder why this one would need an extra shutter speed wheel, when the linking system is hidden inside?
Yes, photos show quite a few variations, what we don't know is which came first and reliability. Brian May the guitarist is a leading collector etc of stereo cameras, photographs etc, he owns The London Stereoscopic Company, plus he has a scientific background albeit a PhD in Astro Physics. I kow he;s done course in early processes at Dimbola House, Isle of Wight, UK, the house of Julia Margaret Cameron now a museum with small workshop facilities.