I'm thinking of getting a DMT Diafold for field use, but I can't decide which grit combination to get, extra coarse/coarse, coarse/fine, or fine/extra fine. I suspect that the fine/extra fine would be the best for daily touch up of a relatively sharp knife, but what about if you were in the field for an extended period of time, possibly a survival situation, giving your blade some hard use and this was the only sharpener that you had. Which would you choose? Would the fine/extra fine be able to repair a chipped or badly worn edge, given a little extra time and effort, or would you need one of the coarse grits? If I go with the coarse/fine will I be able to get a durable edge without the extra fine? I've never used a diamond hone before, so I don't know what type of performance to expect. Any advice would be appreciated.