Hi... Bought a refractometer a couple of weeks ago. Used for a big brew day with club members and in two successive boils afterwords and seemed to be fine. All readings were in the range of predicted gravity.
I have a brew that has been fermented for a week and got a reading of 1.036 on the refractometer which alarmed me (OG was 1060). So I checked against my hydrometer which is reading 1020. Checked the calibration with distilled water, seemed OK. Then checked another of my beers that has been sitting in fermenter for three weeks and again got a 15/16 degree differential. Site glass looks fine with no residue or scratches or cloudiness and from previous couple of brews it seemed fine, so I am confused.
If the refractometer was off from the beginning than the last 5 brew's OG this was used for were all off by 15 degrees, which I don't believe they were given the calculations before the brew. This discrepancy has only come to my attention this last week checking the FG of the last three beers I brewed.