This derailleur was sold in the UK (as this example was) as the ‘GB Altenburger’ and in Germany, possibly, as the ‘Altenburger Tourist’. I have been told that this model was sold as a cheaper version of a derailleur that I have called the Altenburger Champion. I am slightly dubious about this theory - there seem to be too few differences between the two to justify providing the choice. My personal view is that this version (with one stop) is an earlier variant, and the other version (with two stops) is a later variant.
Compared to pull-chain derailleurs of the time this Altenburger is a precise, rigid, parallelogram design. Compared to the Campagnolo Gran Sport it is extremely light and makes extensive use of aluminium.
It has its foibles; the pulley cage pivot, positioned as it is, it does not look as though it has a very high capacity, there are a number of casting flaws in this example, and, unlike the Campagnolo Gran Sport, this version only has one adjustment screw - for the high gear position. Perhaps the low gear stop was provided by stop clamped onto the gear cable as on one of Altenburger's earlier designs.
For some reason Altenburger did not push sales of their derailleurs, preferring to concentrate on their very successful brakes. Nevertheless, it is a sophisticated piece of equipment for its time.