Calculated pivot table field using pivot table data in calculation

Hi all I am new to this forum and have searched and search for a solution to my problem. I have not been able to find it so I apologize for if it has been asked before.

I would like to create a calculated field in my pivot table that is based on the results of a different pivot table field (which could be in a separate pivot table if necessary). I am currently having to manually place a getpivotdata equation into my worksheet

Worksheet columns (Bold values are fixed): plate, organism, fraction, ug/ml, control, abs, abs-blank, abs/gc

abs-blank is calculated as: abs-(average abs of for a particular plate and organism)
abs/gc is calculated as: (abs-blank)/(average(abs-blank) for a particular plate and organism)

Maybe I need a macro to do this I am not sure. I would greatly appreciate any assistance! THANK YOU IN ADVANCE!!!!!!!!!!

Highlight a cell anywhere in your pivot table. Click on the "Options" tab in the ribbon. In the "Calculations" section, click "Fields, Items & Sets". Select "Calculated Field". Name your field and define the calculation you want. Add and you should be set.

Thank you very much for the advice. Unfortunately, when inserting the calculated field I am trying to insert requires the the pivot table to get data. Within each organism I have multiple plates. Each plate has multiple fractions of which blank and gc are two. I would like to use the average of the abs for the blank of a specific plate to calculate abs-blank for only that plate. Similarly the average abs-blank for the gc of a specific plate is used to calculate the abs/gc. I have cut out all of the nonessential data but my file is still to large to attach. I think it may be easier to understand what I am trying to accomplish if you see the file, so I can email it to you if it would help.

Again thank you so much for your help!