The Analox Oxygen Analyser (O2EII) is used in conjunction with the Factair F2235 to test breathing gas and should be held by all service diving branches. Annex K to BRd 2806(5) provides full details of how they can be demanded through the stores system including the NSN.
A number of units have reported that they have received unserviceable Analox Oxygen Analysers. This is due to the oxygen cells which form a key component of the analyser reaching the end of their shelf life. Fortunately replacement cells can also be demanded through the stores system using the NSN 6515-99-1485260 and then replaced by users.
The manufacturer has provided a video on youtube which shows how this can be done: