That's a good point. I've been reading a lot about these Milwaukee refractometers. Seems that temperature is a recurring issue with readings being off. Some say to set your sample out to cool down to room temperature before testing. Another says to keep your calibration fluid bottle in a ziplock bag and put it in your sump for an hour to bring the temperature up. I've tried the first option so far and the result was much better. Granted 0.001 isn't a huge amount but it's half of what it was off by yesterday which is significant to me.