To better control the air on the Progress Hybrid, I closed the air control completely, took a magic marker and put a line on the casting next to the air control lever. This is now the closed position. Then I put additional lines in 1/4" increments to show various degrees of opening. I now have a scale for setting air control relative to the type of burn that I am looking for. The heat of the stove has no impact on the marking-they do not burn off and I now have repeatable references. Simple- I don't know why it took me 2 1/2 seasons of burning to think of it.