There is only one country which is the United States of America.
Some countries in Africa used the customary legal system. They usually use a combination of a customary system and a civil code.
In many European countries the metric system IS the customary system!
The UK uses the predecessor to US Customary called 'Imperial' - most of which is identical apart from volume measures.
Officially, three do: Myanmar, Liberia, and the USA.
There is exactly 2 the metric system and the customary system
44.34375 ml in 3 Tbs
Piecemeal, over centuries and from across many countries - although the UK had a disproportionate share of units.
All of them. Whatever units a country uses are 'customary' in that country.
The metric system is used by most countries around the world, including all of Europe, Canada, Australia, and many others. The customary system, also known as the imperial system, is primarily used in the United States, Liberia, and Burma (Myanmar).
Not everybody will eat meat with wine. In many European countries it is customary to drink red wine with meat but this is not essential.
3 Significant figues are any other number apart from 0
Sports are not a specific custom, but sports themselves have customary behaviors both on and off the field. For example, in many cultures and countries there are customary behaviors and traditions observed by the fan bases. On the field customs include good sportsmanship and respecting the dignity of opposing players, for example.