The optional calibration adapter accessory can be used to feed a reference gas to the probe through a gas port when calibrating. Gas flow should be in the range 0.5–1.1 l/min, recommendation is 1 l/min. Allow the measurement to stabilize for 3 minutes before starting the calibration.DRW244827SP calibration adapter with probe inserted 1 O-ring inside the adapter 2 Gas outlet on each side of the adapter 3 Gas port (port outer diameter 4.6 mm, port hole inner diameter 2 mm, suitable for tubing with 4 mm inner diameter)