insert horizontal knob mystery

[mdl202]

We have a lovely fireplace insert with a completely corroded information plate and two knobs. Being previous warm weather folk we are a bit at a loss. The blue circle is definitely the flue, but the horizontal at the bottom (red circle) is baffling. Could this be an outside air knob? Is one direction typically open? How can you even tell? We are trying hard to become fireplace users but haven't progressed much beyond a puttering flame and smoky living room. Chimney is confirmed clear. Any info is very very appreciated, we have googled everything we can think of. Thanks!!

 

[Woody Stover]

Maybe it's a bypass, which you would open while getting the stove up to the temp required to reburn the smoke. Once the stove is hot enough, you would close the bypass and route the smoke through the reburn section. What is inside the box, tubes across the top? If you stick your head in there, and look up around the flue exit, can you see anything happening when you work the blue rod?
What is that blue thing behind the screen, above the doors? It's not a gas stove, is it?