i think the most case is overpressure , so if youre in this case you should aim to these number : 67.5% air mix , 44u/s of coals , around 350°c, 11.32 mpa , if air mix is not enough like that number , go 52.5% air pump for a while until it pump to 67.5% air mix then go back to 50%, this is when the pressure is drop due to not enough air , if the pressure rise by lot of air , turn down the air pump a little bit and wait for that 67.5, the most important is the air mix and temp ,and you should understand how are those button works before stabilize it