This, first, Altenburger design was a cleaned up version of the design covered in the patent that Altenburger bought from Cervino. Altenburger dispensed with the double cable mechanism, introducing a single cable working against a spring.
It is a rigid, well made, derailleur that mounts under the chainstay. The top sprocket stop is not adjustable - it is just a flange that stops the movement of the rod. The low sprocket stop is a small cylinder that clamps on the cable - you can see this in Altenburger's patent.
The way that the chain tension spring is hidden inside the tube, and pulled by a toggle chain (see photos), is devastatingly cunning but strangely unneccesary.
Finally, the patent shows an adjustable cable outer stop - which is not the case with this example.
Browse associated documents.