Abstract: The present invention provides a method and apparatus for controlling the fluid flow bias of continuous, multiple zone processes having gas or vapor comprising atmospheres that are in immediate access to each other. Active control of the fluid flow bias in at least one process zone or control of the overall process fluid flow bias is achieved by applying force to at least one of the zones of the process in a manner which enables such control. A physical or chemical property or a change thereof in at least one process atmosphere is monitored and an appropriate amount of force is applied in response to the monitored property. The monitored property is related to the furnace flow bias by an algorithm, so that the flow bias can be controlled by controlling the at least one chemical or physical property monitored.