To compensate for saturation changes use a correction chart. There is a correction chart for fresh water and another for sea water. Go to Top 4. Oxygen saturation of water is different at different pressures. Correction charts are provided in most instruction manuals.
Many instruments automatically compensate for barometric pressure.
The barometric pressure is either measured by the instrument or entered by the user. Go to Top 5. Zero calibrate the probe by submersing it in a saturated solution of sodium sulfite. Place the probe in the middle of a vortex so that the air can be forced through the membrane quickly. Air can be forced through the membrane faster in a vortex than if the probe were simply sitting out in the air.