I haven't used the thing in ages to be honest. I tried letting the calibration fluid be at tank temp, I tried letting the sample come to room temp. My icp tests match my refractometer not the hanna. Maybe I got a messed up one? I gave up.I calibrate my Hanna to tank temp also. Haven’t checked in awhile but my Hanna would be 1.026 and refractometer was 1.028. I use the Hanna only but mix and keep tank at 1.024. Either way I’m safe.