How to Calculate frequency based on other columns

Please see attached.

In the sample you will find the list of defects (Column D) by production numbers (Column C). (Error Report Data Summary Tab)

What I am trying to calculate are:

- The Top 3 defects by Month
- The Top 3 defects by last 12 months (Total for 12 months, just three bars)

Another task I was trying to do is setup a tab automatically generated by VB, that will Contain , Month/Year, Distinct List of Def Codes (by month/year),QTY of Defects, Total Units Produced and Qty Defects / Total Units Produced
See the "Error List Month" Tab

In this tab I am hoping to have it auto populated from the summary tab that lists out the distinct list of defect's by month along with the sum of QTY for that defect, total units produced (which is the distinct count of Production numbers for that month) and then the calculation in which I am basing my top three on, QTY of Defects divided by Total Units produced (by month).

Then a top three list chart on the right.

The other tab "Error List 12 Months" its essentially the same as the Month version but instead by month its for the last 12 months from the current month.

I really hope this is doable and that my instructions made sense. I really appreciate any time spent on this.

Thank you
Defect Code Sample.xlsx

Just curious if someone can help me get in the right direction to calculate the defects?
Thanks again.