The Nitrous Oxide Flowmeter Kit is used to measure the flow rate of nitrous oxide in an anesthesia system. The expansion chamber in a nitrous oxide flowmeter allows for the pressure of the gas to increase, causing the gas to expand. This expansion is then measured and used to calculate the flow rate of the gas. The flowmeter helps to ensure that the right amount of nitrous oxide is delivered to the patient, helping to maintain a safe and effective level of anesthesia during a medical procedure.