Abstract: Various examples disclosed relate to an apparatus and method for use in verifying input gas, such as differences between a first and a second gas in an anesthesia flow control where one of the gases is oxygen gas and the other of the gases is nitrous oxide gas. The apparatus can include, for example, a chamber having an inlet to receive gas and a vent to exhaust the gas, a gas control to fill the chamber with the gases to a determined begin pressure, and a microprocessor configured to measure respective times to exhaust the first gas and the second gas from the chamber, via the vent, to reach a determined end pressure. Based on time to exhaust the respective gases, a difference between the first and second gases can be identified; this verification can verify that improper crossover/ross-connection of gas supply lines is not present.