Thanks Dave. I know it's only one dive on the Kyarra, but it really was terrific. One of the first things I noticed with CCR is you can breathe as much as you like. With OC you're constantly aware that the bubbles going out will never come back, so you become unconsciously frugal with breathing. Oddly, whilst ferreting around in the wreck, I remembered that you can breathe without affecting your buoyancy and also reduce the amount of percolation (bits falling down from above) as bubbles stir things up. Such a bleeding obvious thing, but it was an unconscious "skill" developed over years of wreck diving using a twinset. I don't know if other common rebreathers encourage you to run the unit manually, but I was shown to run the Revo with a setpoint of 1.2 but run it manually at SP1.3. I like that as it means developing the understanding of fine trimming the oxygen or diluent injection as you work hard or change depth. The orifice (leaky valve constantly injecting a small amount of oxygen) helps in this respect. When stopping to gawk at some blenny/lobbie/whatever or keeping a decompression stop, it will mean the oxygen levels will remain pretty static. So treat a controller's oxygen injection as a tap on the shoulder that you've not kept your eye on the PPO2. Am sorting out my helium stash from my dealer. Think the two twinsets are about to be put to use as diluent and oxygen banks. Already reassessing how many tins I need. Currently I've 3x Ali 7s and 3x Ali80s. Need to do the maffs for bailout calculations as I progress deeper and work out what the best options are. Would guess that for above **60m you'd keep a strongish helium mix and periodically top off with air as it's slowly depleted with bailout testing and bag inflation, e.g. 20/50. Of course for regular diving I'll be cycling scrubbers way more than the sensors say. After all it's only 1.3kg for peace of mind! It is really good to know that the scrubber times are way longer under the sensors than the CE testing rules of thumb. **not yet, only thinking now about the future.