I'm also building this bad boy to pressure test the console out of water down to 5.5 bar or 45 metres - I don't want to do that in water. Just waiting on a pressure relief valve, an adaptor to connect to the BC inflator and a couple of other bits. It will connect up to the scuba cylinder for filling.

I'm waiting on delivery of the pressure relief valve which will fit between the gauge and the housing and the BC Inflator connector. Will need O-Rings and PTFE tape on the threads.

Credit to Michael Macdonald (macado) who originally published this design and build on his website, thanks Michael :-) The only major difference is I'm using the next size up water filter from the same manufacturer.

http://wrecklessdiver.com/building-50-o2-cell-checker/