[colinicky]

Thats the problem I know all the spec figures but with the temp stick in you can go a hell of a lot longer than 2 or 3 hours anyway If your doing a long deep dive first followed by a short second shallow dive then you would probably be ok but if my 2nd was a wreck dive not a drift then i would tend to change sorb anyway .+ if your worried about 2l verses 3l cylinders IMHO it's a none starter either dive it alpinist in which case at 100m 2 verses 3 is the least of your problems or IMO be sensible & carry bail out in which case your bail out would be the same plan anyway .By the way when do you do your course ?