Razer Iskur XL Chair

This may be a silly question, but what is the knob on the underside of the seat supposed to do? I really wish the instructions were in text, because I had trouble trying to decipher the pictographs. Don't they think we gamers know how to read? :) When I first got the chair, I turned that knob counterclockwise, but it didn't seem to do anything at all. Right now, I'm still trying to make the chair comfortable, so I thought I'd find out what this is actually supposed to do. Frankly, the chair is hard as a rock. I'm amazed there isn't a cushioning effect from an air piston when I sit down, as with every other computer chair I've had. But there seems to be no give to it at all. And it's not comfortable when leaning back, either. Admittedly, I just got out of the hospital, so maybe nothing would be all that comfortable right now. I didn't have a chance to use the chair much before then, because the lumbar support was broken. (To their credit, Razer Support was very quick to get me a replacement chair back. I'm grateful for that.) But even when the lumbar support was broken, the seat was remarkably hard. Anyway, I think I've figured out what everything else on the chair does, but I'm still wondering about that large knob on the underside of the seat. Could someone fill me in? How should I set it? Thanks.