If anybody wants to read lots of commentary on units and their definitions, take a look at the data sheets for the Frink language. The ampere and the candela are two of the more irksome ones, as described by the author.

https://frinklang.org/frinkdata/units.txt

Fascinating. Thanks! At one point I wrote a unit conversion program before such things were ubiquitous and I included a field that had information about the units involved. In service of this, I copied a number of older books on measurement units though I never got around to folding most of this into my program.