Abstract: A variable air flow volume conditioned air distribution system of the kind having an air flow duct for supplying conditioned air to a room and a valve in the duct for regulating the volume of air flowing through the duct has a controller which senses the flow velocity in the duct and the room temperature in the room.The controller combines a temperature signal with a flow velocity signal through a velocity spring. A temperature change resets the flow velocity set point and produces a corresponding change in the volume flow through the duct.The controller includes an adjustable bias for the velocity spring for varying the rate of the velocity spring from a low spring rate for control at a low maximum permitted flow velocity in the duct to a higher spring rate for control at a higher permitted maximum flow velocity flow in the duct and vice versa.