Oh, and as Shalmaneser points out, they use chromatography these days. It’s more efficient, requires less training, and tells you more.
Have I missed something?
I thought that the reason that it was ‘% by volume’ was to distinguish it from ‘% proof’.
No, because it isn’t ‘% proof’. Percent is per hundred, and proof is per 200.
Semantics aside, I don’t think proof has a meaning in the US beyond being twice the alcohol % by volume. When was the last time you saw someone burning gunpowder and alcohol to see what concentration it had?
It’s percentage (%) of alcohol and degrees (superscript 0) proof.
And confusingly, 100% alcohol is 200 degrees proof in the US and 180 degrees proof in the UK.