2013 Mazdaspeed 3 knock retard

So I recently picked up a 2013 mazdaspeed 3 and its all stock but my knock retard has been all over the place to 0.00 all the way up to 5.03. From my understanding it should be at 0.00 why is it getting all the way up to 5.03 is there something I should be looking at replacing?