I can tell you a perfect case when cells "fail"high..

say you had one or two cells that had water droplets on the that you didnt see befoe you calibrated... now you calibrate all cells will have the same po2 value once calibrated.. now once the moisture drops off the cells tose two cells will be reading much higher than normal.. now lets assume your cll that is actually calibrated correctly was one that normally has a lower output say 40mv in oxygen, which is perfectly acceptable..

you would look at your sensors and see one is lower than the others and conclude its the bad one.. if all 3 cells are reading about the same hopefully you would conclude you screwed up with the calibration.. If you do a flush with a know mix at a specific depth it will at least tell you if the cells are operating where they are expected to at the depth you are at..

On the HH you dont have to calculate anything just select the fo2 function and it will tell you what the loop is expected to be on a flush, otherwise use a gas you can easily compute,memorize of carry a cheat sheet..