Vaporizers should usually be tested with an oxygen flow of 4 L/min. Nitrous oxide may affect the readings of some vapor analyzers and should not be used). Test the vaporizers at OFF, low, mid and maximum concentration settings. At one concentration setting (e.g., 1.0% for halothane, 10% for desflurane), test the vaporizer at 1 L/min. The concentration should be ±0.3% vapor or ±15% of the selected value, whichever is greater. [If errors in concentration are observed, allow the vaporizer to operate for a minute or two and recheck the unit. Some units may require a short stabilization period.]