What is a Power Rating (PR)
Let me start with the definition of a Power Rating. Let's say you could clone yourself and you would be partners.
A Power Rating is your average game percentage when you are your own partner and you play against average opposition.
To get from your real average game percentage to your Power Rating, I first adjust your average game percentage to show what it would be if you had played against average opposition. This is the DOD number. If your average opposition had a Power Rating of 52, and you played at their level, you have a PR of 52. However the way bridge is scored, you would have a 50% game. So a DOD would be 2, and this is added to your average game %, what ever that is.
Now I split your adjusted game % between you and your average partner. You are 1/2 of this game %, but the split is not 50/50. The split is the same ratio as the ratio between your overall PR, and your average partner's PR.
1/2 PR + 1/2 Part = % + DOD