Don
I have contacted the company that I got the meter from and they told me to contact the manufacture of the unit, which I did in regards to the calibration, unfortunately since the company I bought the unit from just past me off to the manufacture and the manufacture has not returned any of my emails. So I am not sure as to what I will do next, except never to buy off of the company I got the meter from again or from the manufacture of the meter! I did contact the manufacture of the RO/DI unit (Buckeye Field Supply) and they were very helpful and responsive to my issues and understanding of the whole concept and principles of the unit.