Why do we say “the rule of thumb”?

When we want to measure or do something specific in a certain way we will that’s the rule of thumb. But what does it actually mean and where did come from? In the year of 1976 not only the cold war ended but NOW magazine published an article talking about the origins of this expression. They said the expressions spurred in 1782, an English judge said “a man should have the right to beat his wife with a stick as thick as his thumb”. Though there is no truth behind this statement made by the judge. Actually the truth is much more simpler and happier. The reference is used when with no scientific knowledge to prove otherwise. The rule is often used to describe vague things, imprecise things. Much like the thumb which is not a real instrument of measurement.