Trouble with EKGs

[mlbdestined]

I was wondering what the lower right lead is used for when running twelve lead EKGs.

1. Lead I is RA to LA

2. Lead 2 is RA to LL

3. Lead III is LA to LL

4. aVR is RA lead

5. aVL is LA lead

6. aVF is LL lead

and V1-6 are all unipolar leads which completes the 12 lead analysis

Then what is the lower right lead for anyway? I know it's used for something or else we wouldn't put it on obviously. Thanks for the help you guys.

[GilaRRT]

It's your ground.