Calculate % Perfect PO

I want to calculate the percentage of Perfect PO,
For that I have to consider certain criterias like -

  1. Out of a list of WFs, I have to include only 1
  2. Payment should be on time
  3. No manual changes after PO ordered
  4. Some more criterias
    I am struggling to calculate this percentage, could anyone help me with this?
    Thank You.

Best Wishes