WHAT IS THE DIFFERENT BETWEEN PROOF AND ABV ?

Dear curious reader,

Being French I tend to refer to abv more than proof when discussing the alcohol content of a drink. Proof appears from time to time through. But what is the difference ?
Read on to find out !

Both abv. and proof refers to the measurement of the content of ethanol in a liquid. The statement of the measurement is compulsory by law in many countries. That already make two common points.
Where are the difference
- the history
- the calculation

What is "proof”?

Liquor was "proofed" at the distillery by adding gunpowder and lighting it on fire. If it didn't light, the alcohol content was too weak. If it burned yellow, too strong. If it burned blue, the proof was just right (that was around 57 percent, or 114 proof). A century ago, our federal government established a standard that quality spirits were "bonded" at 100 proof, or 50 percent alcohol. You still see the word bonded on certain 100-proof bottles of old brands such as Rittenhouse Rye or Laird's Straight Apple Brandy, but the term doesn't really carry much weigh any longer. Over time, federal and state excise taxes on higher-proof spirits drove down the average proof, as did health concerns and consumer preference. Jack Daniel's whiskey, for instance, dropped from 90 proof to 80 proof in 2004.(1)

What is “abv.” ?

It means alcohol by volume. 

Internationally, the International Organization of Legal Metrology recommends how to measure alcohol strength (2)
It is defined as the number of millilitres (mL) of pure ethanol present in 100 mL of solution at 20 °C (68 °F). The number of millilitres of pure ethanol is the mass of the ethanol divided by its density at 20 °C, which is 0.78924 g/mL. The ABV standard is used worldwide. (4)
However, in France it is underwood differently.
In France, alcohol content is in degrees Gay-Lussac (GL). A technician tests the solution with a hydrometer a hydrometer. Then the person expresses alcohol strength as parts of alcohol per 100 parts of the mixture. Thus, a spirit with 40% alcohol by volume equals 40 degrees GL. (3)


And if my explanations do not make things clearer, here is a last chance: a great tube video !!! (BELOW)

SOURCE
1--http://www.washingtonpost.com/wp-dyn/content/article/2010/07/13/AR2010071301468.html
2 and 3 — . https://www.alcoholproblemsandsolutions.org/alcohol-proof-and-alcohol-by-volume-definitions-and-explanations/
4 — https://en.wikipedia.org/wiki/Alcohol_by_volume