I used to think coolant mix was just a guess, but a job in Detroit proved me wrong
For a long time, I just eyeballed the coolant to water ratio, thinking close enough was fine. Then we got a big aluminum job for a Detroit auto supplier and kept getting rust spots on the parts after machining. The shop lead made us use a refractometer to hit exactly 8% concentration, and the rust stopped completely. Now I check it every Monday, but does anyone else find those little tools hard to read sometimes?
Oh, the blue line... spent a solid week arguing with a refractometer before someone pointed that out. Felt like a real genius trying to read the ghost of a shadow instead. Guess that's what we get for treating precision tools like a magic eight ball for so long.
My old shop in Toledo had the same "close enough" attitude until we started on a batch of custom headers. The cheap test strips we used were always giving different shades of green. Switched to a refractometer and had to learn that the blue line is the one you actually read, not the shadow.
Our old foreman in Dayton swore by those cheap test strips for years. I remember mixing coolant one afternoon and getting three different greens from the same bucket. The refractometer manual was just a blurry photocopy, so we all guessed at the line for a month. It's crazy how something so simple can trip up a whole shop once you're set in your ways.