How to know the sign of the epsylon=dif.V in a source of Electro Motif Force(battery)?

If the direction of the EMF is the same in which you are transversing (from - to +), the dif.V should be a positive= rise in the IR. If the direction of the EMF is the opposite in which you are transversing (from + to -), the dif.V should be negative= drop in the IR.