Like to hear your experiences. Today at work we began to get ready for a Minnesota winter. We like to run a 50/50 mixture of anti freeze to get to somewhere near -35 protection. Decided for some reason to check the 5 different antifreeze testing gauges. One small Napa floating balls, one small Auto zone floating balls, 1 Prestone brand oval shaped gauge with a plumb (vertical) measure pointer and a protection pointer. A copy of the Prestone style purchased from Harbor Freight and one large floating tablet type syringe. The floaters were all kind of similar in reading, the Prestone style similar to each other but way different from the floaters , Example floaters on one truck measure -10 Prestone style -35+. In Minnesota 25 degrees is a big difference. Measurement were done in warmed up system and gauges were rinsed in warm clean water before and after testing. Took it one further and took 5oz. of clean water at around 100 degrees and mixed 6 oz. of new ethylene glycol (green stuff) took readings and still floating balls still like -15 and Prestone style was near -25. According to the manufacture of the antifreeze it should have been like greater than -34. So What gauge do you use?. What would you believe?. The floaters would have like 3 balls all the way floating and one laying on the bottom and one semi floating 1/3 of the way up from the bottom. I know the easy way is to start from zero and flush and fill from empty but these are industrial radiators that hold a lot of anti freeze $$