Overall TER calculation

Is it possible to easily calculate the total TER of my portfolio?

I have added the TER attribute to all securities in my portfolio. But PP is acting a little strange, for example, it would not display the TER on almost any screen except when I created a new taxonomy. I suppose then I would like to create a new column which would be TER*„Actual%“ (the weighted TER of that security), and then the overall TER is the sum of this column.

Is it possible to add a new custom column which is the product of two existing columns to accomplish this, for example?