Flexi Says: The half-cell with the higher reduction potential according to the table will undergo reduction within the cell. The half-cell with the lower reduction potential will undergo oxidation within the cell. If those specifications are followed, the overall cell potential will be a positive value. The cell potential must be positive in order for the redox reaction of the cell to be spontaneous. If a negative cell potential were to be calculated, that reaction would be spontaneous in the reverse direction.