Hi ! To date, I knew of the existence of only the Sievert 925 stove. But I came across one interesting picture showing three similar Sievert stoves. 1 is Sievert 925; 2-Sievert 925-5; 3- ???????? Please tell me what is the name of the third stove? Can you tell which of these stoves is the rarest? And where can you read about these furnaces?