Help with Rega tonearm

I'm in the process of redoing my whole system and am going through my vinyl equipment. I have a Rega tonearm complete with cables but for the life of me I can't recall what model it is. From my research I think it's either a RB600 or a RB700. There aren't any labels on the arm to say which model it is. Does anyone know how to differentiate the models?  I'd like to put it up for sale but want to price it appropriately so this would greatly help.