The problem I found with swing arms is consistency. Take a reading after you think you have it calibrated. Now rinse it with fresh water (as per mfg instructions) and let it dry. Now do another SG
test. Never had two that agreed. As I was testing the SG
of my 125 gallon tank, I know the SG
did not change from 1.026 to 1.022 in a matter of hours, or form one day to the next. Those are the types of swings I would see.
Get a refractometer. Don't use test strips either. They are fine for a swimming pool, but not for a sw