It was supposed to come calibrated. I got mine last year and it read between 22 - 24% moisture. I tried and tried drying out the honey, but could never get it below 19-20%. As a result, I couldn't sell any of the large quantity I had. Instead gave it to friends and family and told them to keep it refridgerated. This year, it was reading about 21% moisture content. However, I entered a couple things in our State Fair in categories they didn't appear to be testing moisture content. I was there while they were doing the judging and my heart sank when I saw they were actually refracting all items, even though only some said they would be. Luckily for me, it turns out the calibration on my "deluxe refractromer" was way off...the State Fair read it at 17.3% moisture (remember, mine read it at 21%?!). Never would have known if it weren't for entering things anyway!...thank goodness I did!
------Response from Betterbee-----------------
Hi Denise, the refractometers are pre-calibrated. However, because they are a manual device they must be checked for calibration when the ambient temperature fluctuates in 5° swings either up or down. The device responds to the ambient room temperature, which can affect the moisture reading. We reccomend following the enclosed instructions to calibrate the device every so often. An alternative to a manual device is a digital one, which can be calibrated with plain water. However, the digital variants are much more expensive.