Here is a non-burned Primus marked as no. 121. It does not look like the other 121's, the cast iron frame has 4 legs and is not as elaborated as the other ones in this folder, or what I have found in catalogues so far. I understand however that these models may have changed a bit in design over the years. It has a few dents in the tank, but apart from that seems ok. Marking "S5" puzzles me. S would suggest 1928, but I do not think the stove looks that old at all. If anyone recognizes the model and knows more about year etc, please share.