I don't understand what the *nstart* changes in the algorithm. 

If `centers = 8`, that means the function will cluster 8 groups. But, what *nstart* variates?

This is the explanation on the documentation:

```
centers:    
Either the number of clusters or a set of initial cluster centers. If the first, a random set of rows in x are chosen as the initial centers.

nstart:
If centers is a number, how many random sets should be chosen?

```