Question

The quality of the petrol is measured

Answer 1

There is no single measure that defines the quality of gasoline.

If you look at the spec sheets for gasoline in the US or EU, they list over twenty different standards that must be met to confirm that a gasoline batch qualifies as salable.

Here are some examples: https://www.chevron.com/-/media/...

Warning: Don’t open this link unless you really want to know details about gasoline specs. If you aren’t interested, it will bore you to death.