Product Price Index

Hello Everyone,

Im trying to calculate a product price index. In my case a Avg. Rolling 12 month measure versus the Avg. Rolling 12 Month price  from 2 years ago (this is the tricky part for me, as my denominador has to be always the January of 2 years ago.)

Formula : (100) * ( Avg.R12M Dec 2018 price  / AvR12M January "2016"*)  

Where January 2016* is the comparison point of my index, and it will always be the start point equal to 100.

I having big problems with setting a dynamic denominator for this formula. it has to consider the actual Avg.12RM let say Dec 2018, and compare it versus the Avg.12RM price of January 2016. 

So basically i need to accomplish 3 steps:

1) Calculate a rolling 12 month of daily prices by product.

2) Create a dynamic measure as initial point of my index: set as January of  2 years ago.

3) Set the a dynamic Line graph that changes acording the denominador to display the correct versus "January" result.

The final formula would be  = (100) * ( Avg.R12M Dec 2018 price  / AvR12M January 2016*), but at the same time being dynamic enough, as next month 2019" it would move the denominator 1 year to become Avg.R12M January 2017.

Any help or suggestions?

Thanks,