Those who chose the high wattage options such as 100, or 250 watt had a mains resistance to cut down power except during exposure which would have been brief. To assist the setting of accurate stops a device was almost unavoidable and needless to say the factory came up with the answer.
VALOO was a clamp on ring fitting over the front plate of a 50mm Elmar, or in an alternative a Hektor, standard lens. A concentric ring grasped the miniscule stop setting block and the device had a duplicate scale engraved where it could be seen.Several types of this basic item exist and they were also produced by Cooke, among others, A simple enough device but just make sure it is intended for your lens otherwise problems will arise. An extension of the use is that the ring can be secured as an effective lens hood. In later days the Elmar became upgraded to a larger item with slots to engage devices on the front ring.The Valoo was so upgraded to a massive ring which finds some uses in close up and bellows work to solve similar problems.
The Code words are VALOO for the small unit from 1948 with click stops and VALAU for the pre war unit without them. This earlier unit was in chrome rather than black and had relative exposure stops i.e 1,2,3,4,6,10. The unit for Hektor is rarer but was coded VOOLQ and only, I think, made pre war. The later code number was 16620. The larger unit is marked VTOOX for Elmar only. It also exists as VTROO for the Summicron. For every one hundred mentions of the small type one sees perhaps one of the larger type- but that does not make them rare or collectable. Rather, they came along when the SLR had commanded the world stage.