diversity is the beauty of reefin. Everyone reef's a little different.
I calibrate by taking my meter over to a buddies house and comparing it to his meter. I see this as good because if his system is doing good then mine is. Also, I get a free beer or two using this method.
You use RODI - although you know it is a couple points off and you should be adjusting for that, it is still a point of reference. Not one that I would suggest to other users to use, but it works. You have proof it works, very nice reef.
The true way, 53ms reference fluid. The guy that uses this is real boring but has a lot of expensive stuff becuase he reef's different. Instead of spending every last penny on frags, he is buying equipment, testing levels. This guy is real boring to me. This guy needs a beer and a lazy boy in his life. It would truely enhance his reefin.
I choose the beer method. It works for me.