Over the years I bought a couple those things that look like a turkey baster with a couple arrows floating in it. It reads the specific gravity of whatever fluid (when you add the antifreeze to water, I don’t remember, but it makes it heavier or lighter per cubic foot). I think when I got them, they were two or three dollars, so they might be $10 now and I’m sure they have them in Australia.
you suck the antifreeze up into it, and hold it up and down so the top needle point straight down, and the side needle will point to the protection level
I have several vehicles, so I use a 6 gallon jug with a Spicket, and I put my antifreeze in there. I add water until it’s good to about 0° or maybe 10 below, which rarely happens in Atlanta. That mix rate is more like 60 or 65% water, and it saves a couple bucks. Then I pour it off in 1 gallon jugs, and I have one jug in each vehicle.
Whatever you do, don’t mix it 65% because of what I just said Using that specific gravity tester is by far the best way.
Hope it helps