well, don't kille me if Im all wrong here, but I belive it's as simple as this:
Name the guy "Rob" in the name field, right?!
Ya could Set a start-rating from yer INIT field, i.e. : "THIS ADDRATING 0"
Then try a trigger :
Cond. : Rating Rob == 12
So it will prolly fire when Rob has got 12
ya could try & test it with another trigger :
Rob addRating 12
...or alike
hope it's true
;D