Blay trifle in Gien earthenware Renaissance décor - regulator

Trivet, blay table stove. Patented sgdg system. It is made of gien earthenware and oak frame. Renaissance décor. Regulator system: I don't know how it works and if it's complete. Model sold without the original cap. Room resting on small casters, which are in good condition. Note that the earthenware tile has enamel wear (friction). I do not know if the "stove" system is functional. Some nails are missing from the galva bottom (this one is still fixed). Overall dimensions: 27 X 27 cms. Dimensions tiled part: 20.5 X 20.5 cms. Height: 7 cms. Weight: 1490 grs. 13223/3.