As we know, the oxygen (O2) and moisture (H2O) levels in glove box are critical for many organic compounds and organic devices (espeically with Calcium layer as electron injection layer in typical OLEDs). In general, the level of O2/H2O is nomitors by certain sensors, ie. 1.0 ppm; such reading value is just some electrical signal generated by the sensor, and it is only trustworthy when the sensor is properly calibrated at the first installation and shows no degradation over time onging, and sometimes it is difficult to tell if the sensors are still working properly or not after 1-2 years.My questions heres are: 1 ) how do we know the actual level of oxygen/moisture in the glove box especially when it is < 1.0 ppm, or other words, how trustworhty is the sensor reading in general? 2) There is off-sets for oxygen/moisture levels in our glove box system, and you can manually change the ppm reading by changing the off-sets. should the off-set be zero, or you can set it to any arbitrary number? 3) is there any quick and pratical methods to check the oxygen/moisture level inside the glove box assuming the sensor reading is incorrect or you want to double check it? I heard of the Ca test ( test the transparency and electrical conductvity of a thin Ca film of 100 nm), any detailed guide about this method?