My SG readings have gone from a steady 1.025 down to 1.022 lately. The only thing that has changed is the temp. It has gone from 80 to 78. Not overnight though, this has been over a week or two period. I have one of the inexspensive refractometers. I calibrated it with RO water and it reads zero. I also checked with tap water just for the heck of it. also 0. My refractomneter is a RHS-10ATC. Does the ATC mean Auto temp compensated? Don't understand whats going on.