This is for the true and original Analox O2EII Pro Replacement Oxygen Sensor. There are a number of ‘alternative’ cells on the market, some of which are cheaper, but none that are designed to mate correctly with the O2EII analyzer. Some of the ‘alternative’ cells we have seen have a potentiometer fitted. Others have temperature compensation components fitted. None of the cells use the same size waterproof membrane as Analox does.