An anesthetic gas delivery system comprising: a gas machine for supplying anesthetic gas to a patient; a scavenger control system that controls a level of vacuum suction to evacuate waste anesthetic gas; and a user interface electronically coupled to the scavenger control system; wherein: the scavenger control system is configured to adjust the level of vacuum suction to adjust an actual flow rate of the waste anesthetic gas through the scavenger control system based on a measured actual flow rate of the waste anesthetic gas external from the gas machine; the scavenger control system further is configured to transmit actual flow rate information corresponding to the measured actual flow rate to the user interface; and the user interface is configured to output the actual flow rate information to convey the actual flow rate information to an operator of the anesthetic gas delivery system, wherein the user interface includes a scavenger flow rate control for receiving an input of a flow rate control command, and the scavenger control system adjusts the actual flow rate of the waste anesthetic gas in accordance with the flow rate control command; wherein the scavenger control system comprises: an air flow sensor positioned external from the gas machine that measures the actual flow rate of the waste anesthetic gas through the scavenger control system; a control valve that is controllable to adjust the level of vacuum suction to adjust the actual flow rate of the waste anesthetic gas; and electronic control circuitry that is configured to receive a measured actual flow rate from the sensor and to control the control valve to adjust the level of vacuum suction based on the actual flow rate measured by the sensor; wherein the electronic control circuitry further is configured to transmit the actual flow rate information corresponding to the actual flow rate measured by the sensor to the user interface. a gas machine for supplying anesthetic gas to a patient; a scavenger control system that controls a level of vacuum suction to evacuate waste anesthetic gas; and a user interface electronically coupled to the scavenger control system; wherein: the scavenger control system is configured to adjust the level of vacuum suction to adjust an actual flow rate of the waste anesthetic gas through the scavenger control system based on a measured actual flow rate of the waste anesthetic gas external from the gas machine; the scavenger control system further is configured to transmit actual flow rate information corresponding to the measured actual flow rate to the user interface; and the user interface is configured to output the actual flow rate information to convey the actual flow rate information to an operator of the anesthetic gas delivery system, wherein the user interface includes a scavenger flow rate control for receiving an input of a flow rate control command, and the scavenger control system adjusts the actual flow rate of the waste anesthetic gas in accordance with the flow rate control command; wherein the scavenger control system comprises: an air flow sensor positioned external from the gas machine that measures the actual flow rate of the waste anesthetic gas through the scavenger control system; a control valve that is controllable to adjust the level of vacuum suction to adjust the actual flow rate of the waste anesthetic gas; and electronic control circuitry that is configured to receive a measured actual flow rate from the sensor and to control the control valve to adjust the level of vacuum suction based on the actual flow rate measured by the sensor; wherein the electronic control circuitry further is configured to transmit the actual flow rate information corresponding to the actual flow rate measured by the sensor to the user interface. the scavenger control system is configured to adjust the level of vacuum suction to adjust an actual flow rate of the waste anesthetic gas through the scavenger control system based on a measured actual flow rate of the waste anesthetic gas external from the gas machine; the scavenger control system further is configured to transmit actual flow rate information corresponding to the measured actual flow rate to the user interface; and the user interface is configured to output the actual flow rate information to convey the actual flow rate information to an operator of the anesthetic gas delivery system, wherein the user interface includes a scavenger flow rate control for receiving an input of a flow rate control command, and the scavenger control system adjusts the actual flow rate of the waste anesthetic gas in accordance with the flow rate control command; an air flow sensor positioned external from the gas machine that measures the actual flow rate of the waste anesthetic gas through the scavenger control system; a control valve that is controllable to adjust the level of vacuum suction to adjust the actual flow rate of the waste anesthetic gas; and electronic control circuitry that is configured to receive a measured actual flow rate from the sensor and to control the control valve to adjust the level of vacuum suction based on the actual flow rate measured by the sensor; wherein the electronic control circuitry further is configured to transmit the actual flow rate information corresponding to the actual flow rate measured by the sensor to the user interface.