The airflow through a harvesting machine is adjusted by calculating a G-factor at a first point on an upper chaffer to determine if it is greater than 1+n, where n represents a desired factor. A blower is adjusted to reduce an airstream if the G-factor is greater than 1+n. A MOG factor is calculated if the G-factor is less than 1+n. The blower is adjusted to increase the airstream if the MOG-factor is less than 1+x, where x represents a desired factor. A MOG-factor is calculated at a second point if the MOG-factor at the point is greater than 1+x and the blower is adjusted to reduce the airstream if the MOG-factor at the second point is greater than 1+y, where y represents a desired factor or adjusted to increase the airstream if the MOG-factor at the second point is less than 1+y.
