How to calibrate probe by exposing it to air. Using Gravity Analog Dissolved Oxygen Sensor.

Hello, even though the method of calibrating the sensor by exposing it to air is not very accurate, I would like to see what the error percentage is.

For this procedure, could you please let me know what the PPM of air to be considered is? I am reading 5.4 to 6.0 PPM by exposing my probe to air. I know it is temperature and pressure dependent. Is there a formula I could use? Thank you.