How to Calculate Article Uniqueness ?

When publishing a new article to our website we want to ensure it is unique.
– unique to our own website at least.
Of course there always similar articles around so there are softwares that calculate the uniqueness of your article.
But how do they usually calculate it – and in particular, how does Google calculate it ?
Here is one approach that I came up with based on what I have read.
1) From the new article, take the first four-word-group ( this will be the 1st, 2nd, 3rd and 4th words )…
How to Calculate Article Uniqueness ?

See original post by jeddiko