help calculating voltage of a battery

[Sparky Bill PE]

Looking at Zn, I don't know when to use the -.67 or the -1.25 I don't know why it has 2 values. 
View attachment 19772
 

 

[P-E]

Looking at Zn, I don't know when to use the -.67 or the -1.25 I don't know why it has 2 values. 
View attachment 19772
 

Does this help (but don't use -0.67)?:

Zn(OH)[SIZE=12.853259086608887px]2[/SIZE](s)+2e[SIZE=12.853259086608887px]−[/SIZE]⟶Zn(s)+2OH[SIZE=12.853259086608887px]−[/SIZE](aq)


−1.245



Zn[SIZE=12.853259086608887px]2[/SIZE]+(aq)+2e[SIZE=12.853259086608887px]−[/SIZE]⟶Zn(s)




−0.7618