Use a refractometer to measure your mix. I think OTC (Owatonna Tool Company) offered one.
Or use a temperature compensating coolant tester. Cal-Van tools offered it but finding a dealer for CV might be tough.
You’re right, they sell one but I suspect it is pricy by the looks of it. The site suggests Pep Boys sells it, so I’ll scope it out. On the other hand, I see Ebay has a ton of them for sale, some specifically meant for auto use. Seems it is also useful for gems, honey, aquariums, etc.
You think you have it bad? I had a young associate (college student) once who was wringing his hands over changing the coolant in the Scout he inherited from his grand dad. I quizzed him about it and he said it too, IIRC, 15 gallons. I said, “don’t you mean 15 quarts?” He answered that it was gallons, that the thing had a water-jacketed transmission and the manual had instructions for towing combines out of fields.
I thought the structure of anti-freeze had been changed several years ago, and could be run as high as 60% if you wanted more cooling or heating protection. If this is correct, it will say so on the jug.
Yep, everyone wants to overcomplicate it. I just use the total capacity of the system, add undiluted antifreeze to provide a 50/50 mix with the water, then any additional to fill the system is pre mixed 50/50. Been doing it that way for 40 years. Then buy a $10 hydrometer for testing once in a while.
We are both on the same page, I am not going to reread the tools but refractomoters, with distilled water, hey this is not rocket science.