Variable Rates based on 2 values

I am looking to setup Variable Rates in Compensation Workbench (R12)  to supply a "recommended range" (CWB Recommended Amount) .

The 1st variable would be to use the performance rating, the 2nd variable would be to use the existing comparatio.

I found some setup in vision that demonstrates a variable rate based only on performance rating.  Do you know if any documentation exists to walk me through using multiple variables?

This is what I am trying to create:

IF the Current Comparatio is between 80 - 90 AND the Performance Rating is "Exceeds" THEN the range displayed should be 4 - 5%

IF the Current comparatio is between 91 - 100 AND the Performance Rating is Exceeds" THEN the range displayed should be 2 - 4 %