2 ways to calculate net standard reduction potential

[TT0]

On chemwiki, they gave 2 equations to find the standard reduction potential of a cell:

E^ocell = E^ocathode + E^oanode

E^ocell = E^ocathode - E^oanode

Why are there 2 equations and when do you use each one?

Thanks

 

[Bystander]

European convention and American convention and before you ask, "No, I can no longer tell you the differences, nor which is to be preferred."

 

[TT0]

Is the first one the American convention? (Im taking the SAT)

 

[Borek]

Unless I am missing something I feel like there is a mistake in these formulas. Sign of the overall cell potential can be a matter of convention, but the absolute potential shouldn't be. I wonder if they did not omit a minus sign in one of the formulas.

 

[TT0]

Would calculating spontaneity of reaction be the 2 reduction potentials just added to each other?