I thought I illustrated that in post #8 (although in reverse).I still do not understand whether it uses its ATC during calibration or not,.
If you calibrate using the 35 ppt standard packet at, say, 20 deg C, and read that same packet at 25 deg C, does it read 35 ppt, or something else?
In the past I have calibrated with the solution at room temperature, and the device measures incorrectly at tank temperature.
I'll do it again shortly both with a new Hanna sachet and with your DIY 3.29%WT NaCl solution made with reagent grade NaCl for comparison.