Q:

If apostrophe-S is possessive, should "it's" be used when referring to an object's possessions or not?

For example, which is correct:

The robot can then compute it's coordinates.

or

The robot can then compute its coordinates.

What's the rule here? It seems a little inconsistent. 

A:

Apostrophe-S is used to form the possessive for nouns only. 
All possessive pronouns are not apostrophized:

his
hers 
its
mine
yours
theirs
ours

