modifier 82 versus 62

I am having trouble deciding which modifier to use.

Pt has Bilateral Mastectomy. One Dr does one side and another Dr in same group
does the other side at same time. ( to keep pt from being under anesthesia for longer than necessary).
I think modifer shoud be 62 but another co worker thinks it should be 82. But we do these at a teaching hospital. The Dr didn't fell the resident was able to do the
procedure without someone watching closely.
Also is there any place that has a good description of when to use each of these modifiers, the more I read the more confused I get

Any help would be appreciated.